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Thoughts On Coca, Cannabis, Opium & Tobacco – Gifts Of The Great Spirit


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Who Wouldn’t Enjoy A Little Brain Moistening?

If your experience with lettuce opium is that it’s all a hype then … first, I used to agree completely, and second, if you’ll read on you may agree that we probably don’t know the whole story and that there may be a lot more to be re-discovered. Also, if you already know and use garden lettuce, Lactuca Sativa and its wild cousin, Lactuca Virosa as herbal medicines, then I hope that this post contributes to your existing store of useful knowledge.

As for the delightful idea of brain-moistening as a property of Lettuce Opium, you’ll find that ancient Iranian medical concept discussed in the research papers at the end of this article.

Dr. John Duncan, an Edinburgh physician who you’ll meet shortly, clearly knew something important in 1810 that has since been lost. 

Not that many of us in the Cannabis culture aren’t already familiar with “Lettuce Opium” but if you, like me, have tried it several times with a big “so what” result, it’s hard to understand how Lettuce Opium was for many years, across continents, considered by physicians and patients alike to be an excellent substitute for Opium itself, without the addiction and side-effects but with many of the virtues – pain relief, a restful night’s sleep, and – in today’s terms – what sounds like a nice high. 

Doesn’t sound like the “Lettuce Opium” of today, dThese early physicians were objective observers, and when Dr. Duncan says that his Lettuce Opium extracts fall somewhere between Bengali and Turkish Opium in their effect, I believe him. 

So why was Lettuce Opium so effective in the 1800s in Europe, where they had their choice of opium opium, and why has it been a respected medicine for thousands of years in Iran, where they have had their choice of opium opium since forever, but today when you buy lettuce opium on eBay or Amazon or at a local head shop it is almost always – in my opinion – a big disappointment?

This question has been circulating in the back of my mind for years and finally, one day quite recently, the answer appeared with discovering this gentle little essay from 1810. It looks like the active principles in Opium Lettuce are far more unstable than those in Papaver Somniferum, and it has to be used somehow immediately after harvest for best results. 

And that fits perfectly with how doctors provided patients with medicines in those long-gone centuries. They didn’t write a script and send the patient off to a pharmacy to buy pills from Pig Pharma. Most doctors in 1810 made many of their medicines themselves or, at a minimum, bought their natural medicines from someone in the community who made them to order. In other words – fresh. I thought – maybe that’s why Lettuce Opium worked so well for these doctors and their patients, and why the Lettuce Opium sold today for a recreational high is by and large a bust.

A little research on the internet confirmed that my hunch seemed correct about the instability of the active principles in Lettuce Opium – they degrade very quickly in a matter of a few days or at most weeks, depending on storage, environmental conditions, the care and media used for extraction, the lettuce species used, etc. That tells me that there are probably great opportunities for home medicinal herb gardens and in local markets and little chance of seeing “Corporate Opium Lettuce” like we’re seeing “Corporate Cannabis”.

So, let’s ask again, what did Dr. Duncan know in 1810 that we don’t get today? Or are we so over-medicated in today’s world that simple lettuce opium is just too mild and doesn’t do it for us? 

I seriously doubt that, because when you look at the 1800s there was a shitload of pure heavy duty opium everywhere so when this doctor compares his fresh lettuce extract as the equal of Bengali but not quite as strong as Turkish Opium you know he’s speaking from experience. 

I smoked a lot of both Turkish and SE Asian opium in Amsterdam in the 90s and I agree with the good doctor from 1810 – there is a definite difference. If lettuce opium was hitting his patients, and the good doctor himself, in 1810 with an impact somewhere between Turkish and Bengali Opium I would have to say that’s not what I’ve experienced today. There’s a mystery to be solved here, which is why I’m sharing this.

With 50-70 million people in the US alone suffering from moderate to severe insomnia and with few if any effective sleep-aids available, I wonder if having this fresh, organic, locally-grown Opium Lettuce solution available, even at local markets, could be an answer to a lot of people’s dreams – quite literally – while reducing their dependence on Pig Pharma. I also have to wonder what role Lettuce Opium might be able to play in helping people work their way free from industrial poisons masquerading as  street drugs. Then there’s a possible role in withdrawal from tobacco product addiction, treating eating disorders, and maybe more. I’ll share some of those references later.

So with that in mind I am offering this short paper by an 18th Century doctor whose experiments with Lettuce Opium clearly point the way, in detail, for anyone today who wants to make potent, fresh, safe and effective Lettuce Opium. The doctor’s directions are clear and simple and I hope that they are inspirational.

Keeping in mind that the good doctor’s outdoor lettuce production was in a garden in cloudy, cool Edinburgh, Scotland it seems clear that Lettuce Opium could be a very effective natural medicine that anyone can grow anywhere and prepare even in a small growing container, or intercropped with other medicinal herbs in a garden.

“Observations on the preparation of Soporific Medicines from common Garden Lettuce”, by Dr. J. L. Duncan, Senior, 

Read in the Caledonian Horticultural Society, 6th March, 1810, and printed in the 1st volume of their Memoirs, p. 160. et seq. 

https://www.biodiversitylibrary.org/item/123537#page/17/mode/1up

“Opium, or the inspissated white juice which exudes from the capsule of the Papaver somniferum, or Opium Poppy, when wounded, has long been allowed to be one of the most useful articles employed in the alleviation or cure of diseases. The high encomium bestowed upon it by the illustrious Sydenham, has been fully confirmed by the testimony of succeeding practitioners in every nation. 

“It is, however, much to be regretted, that there are individuals of the human species, with whom, from peculiarity of habit, opium seldom fails to produce distressing consequences. 

“There are also conditions of disease, in which it may be very necessary to induce sleep, or allay pain, though circumstances occur by which the use of opium at that time is contra-indicated. 

“Hence it has long been a desideratum in the healing art, to discover other powerful quieting medicines. For, although it is hardly to be expected that an article will ever be discovered, so extensively useful as Opium, yet a good soporific may be found, which, with some, will have less influence, either as exciting sickness at stomach, as occasioning confusion of head, or as inducing a state of constipation. 

“It has been the opinion of many that all the milky juices spontaneously exuding from wounded vegetables possess somewhat of the same sedative power with the milky juice of the poppy. Few plants in Britain afford such milky juice more copiously than the common garden lettuce, the Lactuca sativa of Linnaeus. 

“As everyone must have observed, that this juice when spontaneously inspissated by the heat of the sun on the wounded plant, soon assumes the dark colour of Opium; while, at the same time, it possesses in a high degree the peculiar, and, I may say, specific taste, which distinguishes that substance. Besides this, it is a well-known fact, that lettuce was much used by the ancients as a soporific. 

“These circumstances led me to turn my thoughts on some method of collecting and preparing this exudation, that I might try its effects in the practice of medicine. And, after several trials of different modes of preparation, those which I shall now briefly describe are the best methods I have yet been able to discover. 

“I dedicated to this experiment, in my garden at St. Leonard’s Hill, near Edinburgh, a small bed of that variety of lettuce, which is commonly known among gardeners by the name of ice lettuce. I allowed the plants, about a hundred in number, to shoot up, till the top of the stem was about a foot above the surface of the ground. I then cut off about an inch from the top of each. The milky juice immediately began to rise above the wounded surface. 

“Though then of a white appearance, it had next day formed a black, or dark-coloured incrustation, over the surface where the stem was cut off. I found it impossible to separate this by scraping, as is done with the milky juice exuding from the head of the poppy, when it has assumed the form of Opium. 

“I therefore cut off with a sharp knife a thin cross slice of the stem, to which the whole of the dark coloured opium-like matter adhered. This was thrown into a wide-mouthed phial, about half filled with weakened spirit of wine, the alcohol dilutum of the Edinburgh Pharmacopoeia, formed of equal parts of rectified spirit (grain alcohol 190 proof) and water. By this menstruum, the whole black incrustation on the thin slice of the stalk was dissolved; and the spirit, as may be readily concluded, obtained both the colour and taste of the black incrustation. 

“Each of my plants, in consequence of the fresh wound inflicted by the removal of the thin cross slice, afforded a fresh incrustation every day. And by throwing these into the phial, I soon obtained what I concluded to be a saturated solution of the exudation from the lettuce, or rather of the milky juice in its inspissated state. It was then strained off, to separate the pure solution completely from the thin slices of the stalk. To this strained spirit, which had nearly both the appearance and taste of the ordinary laudanum of the shops, I have given the name of solutio spirituosa succi spissati lactucot

“From trials made with this solution, both on myself and others, I have no doubt that it is a powerful soporific. But to obtain a form in which it might be exhibited, with greater certainty as to the dose, I evaporated the spirit, and thus brought the residuum to a dry state. 

“In this state, it has very much the appearance of the Opium imported into Britain, particularly of that which is imported from Bengal, and which is a much softer substance than the Turkey opium. To this Opium-like substance, I have given the name of lactucarium. And from some trials which I have made with it, when exhibited under the form of pills, it appears to me to be little inferior in soporific power to the Opium which is brought from Bengal, which in general is much inferior in power to Turkey Opium. 

“From the lactucarium thus obtained, I have formed a tincture, by dissolving it to the extent of one ounce in twelve of weak spirit, which is the proportion of Opium to spirit in the liquid laudanum of the Edinburgh college. To this formula I have given the name of tinctura lactucaril. 

“I consider it as the best formula I have yet been able to contrive for obtaining the soporific and sedative powers of the lactuca sativa. And in different cases, I have, I think, seen manifest good effects from it, both as inducing sleep, allaying muscular action, and alleviating pain, the three great qualities of Opium, which demonstrate it to be one of the most powerful sedatives. 

“At present, however, I intend nothing more but to communicate to the Caledonian Horticultural Society a method of preparing a soporific medicine from common lettuce. For ascertaining more fully its medicinal effects, I am at present engaged in a series of trials, which may, perhaps, be like-wise communicated to them. 

“Meanwhile it will afford me great satisfaction, if the above short account shall draw the attention of others, particularly of professional gardeners, to the same subject, and shall lead to the discovery of a better method of obtaining a useful medicine, from a plant so easily cultivated in every garden.” 

Editor’s Note: I haven’t yet been able to find any information on Dr. J. L. Duncan’s subsequent trials aimed at refining his technique and testing his medicine. They’re either lost in time or still waiting to be found. 

However, here is an excellent article in the Caledonian Society papers of 1825, 15 years after the article above. Scroll to page 153 in the manuscript (162 in the sidebar) to begin reading the extremely informative and worthwhile article that talks about Dr. Duncan and others involved in the Opium Lettuce quest. 

Further observations on the Preparation of Soporific Medicines from Common Garden Lettuce.

By Mr John Young, Fellow of the Royal College of Surgeons of Edinburgh.”

John Young’s Method of preparing the Inspissated Juice of Lettuce

“Take any quantity of the leaves and stalks of the lettuce when the plant is nearly ready to flower.

“Bruise them well and including them in a Hempen bag compress them strongly till they yield their juice.

“Let this juice be evaporated in flat vessels heated with boiling water.

“Let the evaporation be continued till the expressed juice be reduced to the consistence of thick honey

“According to the trials which I have made twelve pounds of lettuce will yield about eight ounces of inspissated juice”

John Young’s Method of preparing the Tincture of Lettuce Leaves

or

The tinctura foliorum siccatorum Lactuca Sativæ

“To one ounce of the dried leaves and stalks of the lettuce cut down add eight ounces of the diluted alcohol of the Edinburgh Pharmacopeia ( Editors note: that is a solution of ⅓ grain alcohol and ⅔ distilled water)

“Let the vessels containing this mixture be kept for a week in a warm place shaking it frequently

“Let the liquor then be strained through paper and kept for use”

John Young’s  Method of Collecting The Milky Juice

“It occurred to me that the milky juice of the lettuce might be immediately collected from the plant in great abundance by absorbing it on cotton soon after it exudes from the plant and while it yet continues in a liquid state and by afterwards inspissating it by a moderate heat communicated from a water or vapour bath

I accordingly adopted that method this year – 1816.

I had the ice lettuce planted in rows and when the top of the stem was about a foot above the ground I then cut off about an inch from the top of each plant

The milky juice immediately began to rise above the wounded surface

I cut off the tops of all the plants before I began to collect. But after the portion which had exuded was removed by the cotton I found that the milky juice ceased to exude until I had made another wound

I began to collect at the end of the border where I made the first incision and then cut off a thin cross slice from the stem of each plant leaving fresh wounds as I went along

These I found covered with milky juice each time when I returned to where I set out

After going round the plants about five or six times in the way mentioned they ceased to give out any more milky juice at that time

But this process may be repeated two or three times in a day In the manner above described

In the manner above described I have collected more of the milky juice in one day than I did last year in five days when it was not removed till it had acquired a dry state and black colour

Having mentioned to a friend my mode of collecting the milky juice in its recent state by means of cotton, he suggested the use of a lightly moistened sponge for that purpose instead.

This I find answers better than the cotton; the juice being both more completely removed from the plant, and more easily expressed than from the cotton. The milky juice collected in this way squeezed into a tea cup or any similar vessel, soon acquires a dark-brown colour like opium obtained from the papaver somniferum, and has all its other sensible qualities.”

REFERENCES

As icing on this sweet little cake here are some interesting current scientific references. 

1. “Pilot study of the efficacy and safety of lettuce seed oil in patients with sleep disorders”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3119588/

“Results: Improvements in the modified State-Trait Anxiety Inventory and the Sleep rating scale scores were significantly greater in patients receiving L. sativa seed oil compared with those on placebo (P < 0.05). No side effects were found to be attributable to L. sativa seed oil at the given dosage.”

2. “Evaluation of sedative effects of an intranasal dosage containing saffron, lettuce seeds and sweet violet in primary chronic insomnia: A randomized, double-dummy, double-blind placebo controlled clinical trial”

https://www.sciencedirect.com/science/article/abs/pii/S0378874120329974

“Our study revealed a significant reduction in Insomnia Severity Index and Sleep Quality Index scores from baseline… Moreover, the use of hypnotic drugs in the intervention group was significantly reduced (P < 0.001), while in the control group was maintained at baseline level.” 

Ed. Note: these results show less dependence on sleeping pills (hypnotic drugs) among those receiving the nasal treatment with saffron, sweet violet and lettuce seed oil. These were extracted in almond oil according to ancient Iranian techniques.  Here’s some interesting validation of Saffron & Sweet Violet Oil.

“The Impact of Saffron on Symptoms of Withdrawal Syndrome in Patients Undergoing Maintenance Treatment for Opioid Addiction in Sabzevar Parish in 2017”

https://pubmed.ncbi.nlm.nih.gov/29359178/

“Efficacy of Viola odorata in Treatment of Chronic Insomnia”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4341349/

3. “Analysis of Fatty Acid Composition of Crude Seed Oil of Lactuca sativa L. by GC-MS and GC Methods”

https://tips.sums.ac.ir/article_42253.html

Ed. Note: Before going into lettuce seed oil data and analysis, which show very interesting properties, the author covers the history of the use of medicinal lettuce opium in Iran. He says:

“In Traditional Iranian Pharmacy books, garden lettuce is named “Kass Bostani” and  Hakim Aqili classified it as a “Ghazā’ye Dawā’ee” (Ghazā means Food; Dawā means Drug). It is said to be soporific, prescribed to cure insomnia and to be useful in thirst and feeling of hotness and burning in the stomach. Seeds of this herb reduce semen, suppress libido and are useful in cases of frequent nocturnal emissions. Fixed oil obtained from seeds of this plant is reputed to have hypnotic and brain moistening properties. “

Final note: Don’t know about you but I think brain-moistening sounds promising. Happy salads!


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Forest Bathing Scientifically Validates The Cannabis Entourage Effect

Introduction

The extensively-studied phenomenon known as “Forest Bathing” in Japan and South Korea and as “Kneipp Therapy” in Germany involves exposure to high concentrations of naturally-occurring aerosolized phytochemicals in conifer & deciduous forests.

This natural treatment for conditions ranging from asthma to dermatitis has been documented and validated by a raft of high-quality medical and scientific research.

There is no question that “Forest Bathing” has therapeutic benefits. For example, positive effects on NK (Natural Killer) cell activity have been shown with in vitro treatment of tumor cell lines with monoterpenes released from trees (and of course present in Cannabis flowers) such as d-limonene and α-pinene, and also in forest bathing trips. The anti-tumor effects act by increasing intra-cellular levels of anti-tumor proteins such as perforin, granulysin, and granzymes A/B.

Haven’t heard of “Forest Bathing”? I hadn’t either until I ran across it during some intense research into naturally-occurring environmental Cannabis terpene aerosols. The ancient Japanese natural health practice called “Shinrin Yoku”, defined as “taking in the forest atmosphere” or “forest bathing”, has a wide range of rigorously tested and proven health benefits.

In 2005 the Japanese government introduced a nationwide “Therapeutic Effects of Forests Plan” that pays “Forest Bathing” health benefits. The government says that it pays for this therapy because of the proven reduction in other health care costs across the spectrum.

South Korean scientists and public health researchers have documented a wide range of positive health benefits from exposure to terpenes in the air of coniferous forests, with variations among the terpenes in different species of trees at different locations accounting for differences in the health benefits of inhalation of forest air.

They have divided the country into numerous micro-climes where particular combinations of coniferous tree species co-exist and perfume the air, each location offering a particular healing, stimulating mix of terpenes and other phytochemicals.

Interestingly, the dominant terpenes in the air of these forests are the same terpenes that characterize different Cannabis strains and the same kinds of variability in Cannabis strains similarly account for their differing health benefits.

There is also a natural medicinal therapy in Germany called “Kneipp Therapy”, that involves a series of exercise routines done in a terpene-rich forest environment. Kneipp Therapy has been studied using quality clinical research protocols and the exercises have been found to be significantly more beneficial when performed in a forest environment compared to other kinds of locations. 

So, it’s both very interesting and very significant for establishing the validity of the Cannabis “Entourage Effect” that the dominant terpene profiles of all of the therapeutic forests studied in the Japanese and Korean “Forest Bath” scientific literature (cited below) appear to be various combinations of myrcene, pinene, limonene, linelool, and a number of less-celebrated but still important Cannabis terpenes like cynene, terpinene and boneal. There are many other “minor” phytochemicals shared between the airborne perfumes of Cannabis flowers and therapeutic forests, and almost certainly many of these will ultimately be shown to play significant roles in both the Forest and the Cannabis “Entourage Effect”.

Bottom line – I believe that there is an inescapable argument in favor of the Cannabis “Entourage Effect” presented by the “Forest Entourage Effect”, which itself is definitively established in international, if not US, scientific and medical literature.

Discussion:

There has been extensive research in multiple advanced countries on the health benefits of exposure by inhalation and skin absorption to the airborne terpenes in forest environments – interestingly enough, these turn out to be the same terpenes that are inhaled in the vapors from Cannabis flowers.

“Forest Bathing” research establishes that inhaling a naturally-occurring mix of terpene emissions or vapors has far greater health benefits than exposure to or ingestion of any of the terpenes and other phytochemicals singularly, like in a pill or other oral or topical medication.

Cannabis visionaries have always known that the THC was only one element of the sensual pleasures and only one of the sources of health benefits from the sacred flower, just as wine lovers have always known that the alcohol is only a relatively small part of their total experience. Nobody drinks a bottle of Etude Pinot Noir or Chateau Pomerol Bordeaux for the alcohol, and nobody chooses which Cannabis flower to enjoy simply on the basis of THC content, although that approach seems to dominate much of today’s adolescent-style Cannabis marketing. Even the most dedicated couch-locked stoner knows very well that there is a world beyond THC and may spend a lot of time (if they’re not too ripped)  thinking about taste and aroma options when they’re choosing between Durban Poison and Granddaddy Purple.

However, the concept of a Cannabis “Entourage Effect” has been universally ridiculed by anti-Cannabis forces who say that the supposed variety of effects of different Cannabis strains is simply a kind of mass delusion.  They claim that there is no evidence that different phytochemical profiles of different Cannabis strains signal different health and well-being effects, and say that in their expert, informed scientific opinion such observations are imaginary. While their criticisms are couched in the careful, apparently rational language of science, and even rated a major article in Scientific American in 2017, all of the criticisms amount to a simple “It’s all in your head” dismissal.

In other words, the anti-Cannabis establishment says tough, there’s no scientific evidence to support your claim, and there’s not going to be any evidence either because we aren’t going to fund research.

Well, I’ve got some news for these die-hard prohibitionists.

OK, they have managed to impede research that could validate many of the medical benefits of the whole Cannabis Flower as opposed to plain old THC extract. With notable medical research exceptions, many of the health and sensual benefits ascribed to the Cannabis Flower are currently only validated by experience and consensus, both of which the scientists are fond of reminding us can be way off target. They point to the flat earth delusion, or to many other instances where “everybody knows” something that simply isn’t true, and smugly point out that nobody can prove all these marvelous things we’re saying about Cannabis.

It’s hard to find a reasonable explanation of why the Federal government has arrayed its dark-side powers against the Cannabis flower, but in this match between the Flower and the Power it’s beginning to look like the Power is going to lose this one because Forest Bathing research actually provides plenty of evidence . The research unequivocally supports the validity of the “Entourage Effect” by demonstrating that naturally-occurring environmental terpene and phytochemical aerosols do have measurable, verifiable positive impacts on overall health as well as on specific diseases and conditions, and do vary among forest tree species and environments in the same ways that Cannabis flowers vary among strains in response to environmental variables.

Forest Bathing research is directly applicable to validating the “Entourage Effect” of Cannabis terpenes and phytochemicals that are widely observed but, according to the Federal propagandists,  not “scientifically verified”. As an example, there is solid research that says that terpene emissions from plants are directly correlated with the concentration of terpenes in the plant. The higher the concentration of terpenes, the greater the emissions from the plant. “Forest Bathing” research naturally focuses on terpene emissions from coniferous and to a lesser degree deciduous trees, but the relationship between terpene concentrations and emission rates has been widely replicated in studies with agricultural crops and seems to apply to all plants.

The bottom line is that clinical literature as well as popular wisdom in several countries points to the health benefits of inhaling and “bathing in” an atmosphere rich in terpenes and other phytochemicals. While the health benefits of many of the individual components of this phyto-soup are only recently becoming well-known, the benefits of exposure to the entire environmental complex of a pine/conifer forest are familiar to anyone who has ever walked outdoors that first morning in a forest campground.

A recent study concluded: “Exposure to natural environment is beneficial to human health. Among environmental exposures, the effects of forest have been emphasized in many studies. Recently, it has been shown that a short trip to forest environments has therapeutic effects in children with asthma and atopic dermatitis. Based on these studies, healthcare programs to use forest have been developed in several countries. Forest bathing has beneficial effects on human health via showering of forest aerosols. Terpenes that consist of multiple isoprene units are the largest class of organic compounds produced by various plants, and one of the major components of forest aerosols. Traditionally, terpene-containing plant oil has been used to treat various diseases without knowing the exact functions or the mechanisms of action of the individual bioactive compounds.”

So, it’s clear that relaxing for a few hours in a forest environment filled with terpenes can be beneficial and even therapeutic for people with a wide range of diseases and conditions from dermatitis to cancer. Do a simple internet search for “forest bathing’ and you’ll find books, resorts, videos and even classes. But enter “cannabis bathing” into a search and you’ll get bath salts, bubble bath, and a lot of fruit-flavored massage and lubricating oils.

For the past year or so I have been exclusively using a vaporizer to enjoy Cannabis flowers and I can add my experiences to the observations of many others that whole flower Cannabis vapor is a marvelous clean, natural high which, now that I realize it, is almost exactly like stepping out of my tent high in the pine forests of the Oregon Cascades and inhaling that first breath of vibrant, aromatic, high-energy mountain air.

So in my opinion all this research on “Forest Bathing” makes the smug “You can’t prove it and we’re not going to let you” chant of the anti-Cannabis “scientists” pretty much irrelevant. Sooner or later there will actually be research on every aspect of inhaled and absorbed Cannabis terpenes and other phytochemicals but until then the parallel research on Forest Bathing should be more than adequate scientific evidence for any reasonable person of the validity of the Cannabis “Entourage Effect”.

Selected Bibliography

Frumkin H. Beyond toxicity: human health and the natural environment. Am J Prev Med. 2001;20:234–240. doi: 10.1016/S0749-3797(00)00317-2. [PubMed]

Tsunetsugu Y, Park BJ, Miyazaki Y. Trends in research related to “Shinrin-yoku” (taking in the forest atmosphere or forest bathing) in Japan. Environ Health Prev Med. 2010;15:27–37. doi: 10.1007/s12199-009-0091-z. [PMC free article] [PubMed]

Seo SC, Park SJ, Park CW, Yoon WS, Choung JT, Yoo Y. Clinical and immunological effects of a forest trip in children with asthma and atopic dermatitis. Iran J Allergy Asthma Immunol. 2015;14:28–36. [PubMed]

Spievogel I, Spalek K. Medicinal plants used in pediatric prophylactic method of Sebastian Kneipp. Nat J. 2012;45:9–18.

Joos S, Rosemann T, Szecsenyi J, Hahn EG, Willich SN, Brinkhaus B. Use of complementary and alternative medicine in Germany: a survey of patients with inflammatory bowel disease. BMC Complement Altern Med. 2006;6:19. doi: 10.1186/1472-6882-6-19. [PMC free article] [PubMed]

Kawakami, K., Kawamoto, M., Nomura, M., Otani, H., Nabika, T., & Gonda, T. (2004). Effects of phytoncides on blood pressure under restraint stress in SHRSP. Clinical and Experimental Pharmacology and Physiology, 31, S27–S28.

Li, Q., Kobayashi, M., Wakayama, Y., Inagaki, H., Katsumata, M., Hirata, Y., Hirata, K., Shimizu, T., Kawada, T., & Park, B. (2009). Effect of phytoncide from trees on human natural killer cell function. International Journal of Immunopathology and Pharmacology, 22, 951–959.

Li, Q. (2010). Effect of forest bathing trips on human immune function. Environmental Health and Preventive Medicine, 15, 9–17.

Ormeño, E., Gentner, D. R., Fares, S., Karlik, J., Park, J. H., & Goldstein, A. H. (2010). Sesquiterpenoid emissions from agricultural crops: correlations to monoterpenoid emissions and leaf terpene content. Environmental Science & Technology, 44, 3758–3764.

Park BJ, Tsunetsugu Y, Kasetani T, Kagawa T, Miyazaki Y. The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): evidence from field experiments in 24 forests across Japan. Environ Health Prev Med. 2010;15:18–26. doi: 10.1007/s12199-009-0086-9. [PMC free article] [PubMed]

Song C, Ikei H, Miyazaki Y. Physiological effects of nature therapy: A review of the research in Japan. Int J Environ Res Public Health. 2016;13:E781. doi: 10.3390/ijerph13080781. [PMC free article] [PubMed]