Chapter 25

CHEMISTRY AND TOXICOLOGY OF MUSHROOMS.

By J. F. CLARK.

Regarding the chemical composition of mushrooms, we have in the past been limited largely to the work of European chemists. Recently, however, some very careful analyses of American mushrooms have been made. The results of these investigations, while in general accord with the work already done in Europe, have emphasized the fact that mushrooms are of very variable composition. That different species should vary greatly was of course to be expected, but we now know that different specimens of the same species grown under different conditions may be markedly different in chemical composition. The chief factors causing this variation are the composition, the moisture content, and the temperature of the soil in which they grow, together with the maturity of the plant. The temperature, humidity, and movement of the atmosphere and other local conditions have a further influence on the amount of water present.

The following table, showing the amounts of the more important constituents in a number of edible American species, has been compiled chiefly from a paper by L. B. Mendel (Amer. Jour. Phy. =1=: 225--238). This article is one of the most recent and most valuable contributions to this important study, and anyone wishing to look into the methods of research, or desiring more detailed information than is here given, is referred to the original paper.

TABLE I.

===================================================================+ | FRESH | IN WATER-FREE MATERIAL. | | MATERIAL.| | -------------------------------------------------------------------| | W | D M | T N| P N| E E| S I P A| F | A | | A | R A | O I| R I| T X| O N E L| I | S | | T | Y T | T T| O T| H T| L R C| B | H | | E | T | A R| T R| E R| U 8 O| R | | | R | E | L O| E O| R A| B 5 C H| E | | | | R | G| I G| C| L E O| | | | | | E| D E| T| E N L| | | | | | N| N| | T | | | -------------------------------------------------------------------| | % | % | % | % | % | % | % | % | Coprinus comatus |92.19| 7.81|5.79|1.92| 3.3| 56.3| 7.3|12.5| | | | | | | | | | Morchella esculenta |89.54| 0.46|4.66|3.49| 4.8| 29.3| 8.7|10.4| | | | | | | | | | Polyporus sulphureus |70.80| 9.20|3.29|2.23| 3.2| 27.8| 3.0| 7.3| | | | | | | | | | Pleurotus ostreatus |73.70| 6.30|2.40|1.13| 1.6| 31.5| 7.5| 6.1| | | | | | | | | | Clitocybe multiceps |89.61| 0.39|5.36|1.98| 6.0| 57.2| 9.6|11.5| | | | | | | | | | Hypholoma |88.97| 1.03|4.28|2.49| 2.5| 44.4|12.1|13.9| candolleanum | | | | | | | | | | | | | | | | | | Agaricus campestris | 91.8| 8.2|4.75|3.57|3.72| -- | -- |11.6| ===================================================================+

=Water.=--Like all growing plants, the mushroom contains a very large proportion of water. The actual amount present varies greatly in different species. In the above table it will be seen that _Polyporus sulphureus_, with over 70 per cent. of water, has the least of any species mentioned, while the species of _Coprinus_ and _Agaricus_ have usually fully 90 per cent. water. The amount of water present, however, varies greatly in the same species at different seasons and in different localities, and with variations in the moisture content of soil and atmosphere, also with the age and rapidity of development of the individual plant.

=Total Nitrogen.=--The proportion of nitrogen in the dry matter of different species varies from 2 per cent. to 6 per cent. This comparatively high nitrogen content was formerly taken to indicate an unusual richness in proteid substances, which in turn led to very erroneous ideas regarding the nutritive value of these plants. The nitrogenous substances will be more fully discussed later, when we consider their nutritive value.

=Ether Extract.=--This consists of a variety of fatty substances soluble in ether. It varies greatly in quality and quantity in different species. The amount is usually from 4 per cent. to 8 per cent. of the total dry matter. It includes, besides various other substances, several free fatty acids and their glycerides, the acids of low melting point being most abundant. These fatty substances occur in the stem, but are much more abundant in the cap, especially in the fruiting portion. Just what nutritive value these fatty matters may have has never been determined.

=Carbohydrates.=--The largest part of the dry matter of the mushrooms is made up of various carbohydrates, including cellulose or fungocellulose, glycogen, mycoinuline, trehalose, mannite, glucose, and other related substances. The cellulose is present in larger proportion in the stem than in the cap, and in the upper part of the cap than in the fruiting surface. This is doubtless related to the sustaining and protective functions of the stem and the upper part of the cap. Starch, so common as a reserve food in the higher plants, does not occur in the mushrooms. As is the case with the fats, no determination of the nutritive value of these substances has been made, but it may be assumed that the soluble carbohydrates of the mushrooms do not differ greatly from similar compounds in other plants.

=Ash.=--The ash of mushrooms varies greatly. _Polyporus officinalis_ gives but 1.08 per cent. of ash in dry matter, _Pleurotus ulmarius_ gives 12.6 per cent., and _Clitopilus prunulus_ gives 15 per cent. The average of twelve edible species gave 7 per cent. ash in the stem and 8.96 per cent. in the cap.

In regard to the constituents of the ash, potassium is by far the most abundant--the oxide averaging about 50 per cent. of the total ash. Phosphoric acid stands next to potassium in abundance and importance, constituting, on an average, about one-third of the entire ash. Oxides of manganese and iron are always present; the former averaging about 3 per cent. and the latter 5 per cent. to 2 per cent. of the ash. Sodium, calcium, and chlorine are usually present in small and varying quantities. Sulphuric acid occurs in the ash of all fungi, and is remarkable for the great variation in quantity present in different species; e. g., ash of _Helvella esculenta_ contains 1.58 per cent. H_2SO_4 while that of _Agaricus campestris_ contains the relatively enormous amount of 24.29 per cent.

Any discussion of the bare composition of a food is necessarily incomplete without a consideration of the nutritive value of the various constituents. This is especially desirable in the case of the mushrooms, for while they are frequently overestimated and occasionally ridiculously overpraised by their friends, they are quite generally distrusted and sometimes held in veritable abhorrence by those who are ignorant of their many excellent qualities. On the one hand, we are told that "gastronomically and chemically considered the flesh of the mushroom has been proven to be almost identical with meat, and possesses the same nourishing properties." We frequently hear them referred to as "vegetable beefsteak," "manna of the poor," and other equally extravagant and misleading terms. On the other hand, we see vast quantities of the most delicious food rotting in the fields and woods because they are regarded by the vast majority of the people as "toadstools" and as such particularly repulsive and poisonous.

Foods may be divided into three classes according to the functions they perform:

(_a_) To form the material of the body and repair its wastes.

(_b_) To supply energy for muscular exertion and for the maintenance of the body heat.

(_c_) Relishes.

The formation of the body material and the repair of its wastes is the function of the proteids of foods. It has been found by careful experiment that a man at moderately hard muscular exertion requires .28 lb. of digestible proteids daily. The chief sources of our proteid foods are meats, fish, beans, etc. It has been as a proteid food that mushrooms have been most strongly recommended. Referring to Table I, it will be seen that nitrogen constituted 5.79 per cent. of the total dry substance of _Coprinus comatus_. This high nitrogen content, which is common to the mushrooms in general, was formerly taken to indicate a very unusual richness in proteid materials. It is now known, however, that there were several sources of error in this assumption.

Much of the nitrogen is present in the form of non-proteid substances of a very low food value. Another and very considerable portion enters into the composition of a substance closely related to cellulose. A third source of error was the assumption that all the proteid material was digestible. It is now known that a very considerable portion is not digestible and hence not available as food. Thus, notwithstanding the 5.79 per cent. of nitrogen in _Coprinus comatus_, we find but .82 per cent. in the form of actually available (i. e., digestible) proteids, or approximately one-seventh of what was formerly supposed to be present.

The digestibility of the proteids varies very greatly with the species. Mörner found the common field mushroom, _Agaricus campestris_, to have a larger amount of proteids available than any other species studied by him. Unfortunately, the digestibility of the American plant has not been tested. There is great need for further work along this line. Enough has been done, however, to demonstrate that mushrooms are no longer to be regarded as a food of the proteid class.

The energy for the muscular exertion and heat is most economically derived from the foods in which the carbohydrates and fats predominate.

The common way of comparing foods of the first two classes scientifically is to compare their heat-giving powers. The unit of measurement is termed a _calorie_. It represents the amount of heat required to raise a kilogram of water 1° Centigrade. (This is approximately the heat required to raise one pound of water 4° Fahrenheit.) A man at moderately hard muscular labor requires daily enough food to give about 3500 _calories_ of heat-units. The major part of this food may be most economically derived from the foods of the second class, any deficiency in the .28 lb. of digestible protein being made up by the addition of some food rich in this substance.

In the following table the value of ten pounds of several food substances of the three classes has been worked out. Especial attention is called to the column headed "proteids" and to the last column where the number of heat-units which may be purchased for one cent at current market rates has been worked out.

TABLE II.

NUTRITIVE VALUE OF TEN POUNDS OF SEVERAL FOODS.

========================================================================+ |PROTEIDS.|FATS.| CARBO- |CALORIES.|COST.|CALORIES| | | |HYDRATES.| | | FOR ONE| | | | | | | CENT. | ------------------------------------------------------------------------| a. {Beef (round) | 1.87| .88| ----| 7200|$1.50| 48.| | | | | | | | {Beans (dried) | 2.23| .18| 5.91| 15900| .30| 530.| | | | | | | | | | | | | | | b. {Cabbage | .18| .03| .49| 1400| .15| 93.| | | | | | | | {Potatoes | .18| .01| 1.53| 3250| .10| 325.| | | | | | | | {Flour (roller | 1.13| .11| 7.46| 16450| .25| 658.| process) | | | | | | | | | | | | | | | | | | | | | c. {Coprinus comatus | .04| .025| .434| 987| 2.50| 3.9| | | | | | | | {Pleurotus | .051| .042| .828| 1811| 2.50| 7.2| ostreatus | | | | | | | | | | | | | | {Morchella | .094| .05| .306| 955| 2.50| 3.8| esculenta | | | | | | | | | | | | | | {Agaricus | .18| .03| .46| 1316| 2.50| 5.3| campestris | | | | | | | | | | | | | | {Oysters | .61| .14| .33| 2350| 2.00| 11.7| ========================================================================+

The mushrooms have been valued at 25 cents per pound, which is probably considerably below the average market price for a good article. It should also be remarked that the amounts given in this table are the digestible and hence available constituents of the foods. The only exception to this is in the case of the fats and carbohydrates of the mushrooms, no digestion experiments having been reported on these constituents. In the absence of data we have assumed that they were entirely digested.

The beef and beans are typical animal and vegetable foods of the proteid class. A glance at the table will show how markedly they differ from the mushrooms. The latter are nearest the cabbage in composition and nutritive value. The similarity between the cabbage and the _Agaricus campestris_ here analyzed is very striking. The potato is somewhat poorer in fat, but very much richer than the mushroom in carbohydrates.

The figures in the last column will vary of course with fluctuations in the market price, but such variation will not interfere at any time with the demonstration that _purchased_ mushrooms are not a poor man's food. Here we find that one cent invested in cabbage at 1-1/2 cents per pound, gives 93 _calories_ of nutrition, while the same amount invested in _Agaricus campestris_--the common mushroom of our markets--would give but 5.3 _calories_, although they are almost identical so far as nutritive value is concerned.

The same sum invested in wheat flour, with its high carbohydrate and good proteid content, would yield 658 _calories_ or one-sixth the amount necessary to sustain a man at work for one day. The amount of mushrooms necessary for the same result is a matter of simple computation.

Mushrooms, however, have a distinct and very great value as a food of the third class, that is, as condiments or food accessories, and their value as such is beyond the computation of the chemist or the physiologist, and doubtless varies with different individuals. They are among the most appetizing of table delicacies and add greatly to the palatability of many foods when cooked with them. It is surely as unfair to decry the mushroom on account of its low nutritive value, as it is wrong to attribute to it qualities which are nothing short of absurd in view of its composition. In some respects its place as a food is not unlike that of the oyster, celery, berries, and other delicacies. Worked out on the basis of nutritive value alone they would all be condemned; the oyster for instance presents a showing but little better than the mushroom, and vastly inferior, so far as economy is concerned, to the common potato. This, too, for oysters purchased by the quart. The nutritive value of one cent's worth of oysters "on the half shell" would be interesting!

The question of the toxicology of the higher fungi is one of very great theoretical and practical interest. But on account of the great difficulties in the way of such investigations comparatively little has yet been accomplished. A few toxic compounds belonging chiefly to the class termed alkaloids have, however, been definitely isolated.

=Choline.=--This alkaloid is of wide occurrence in the animal and vegetable kingdoms. It has been isolated from _Amanita muscaria_, _A. pantherina_, _Boletus luridus_, and _Helvella esculenta_. It is not very toxic, but on uniting with oxygen it passes over to muscarine. According to Kobert the substance formed from choline on the decay of the mushrooms containing it is not muscarine, but a very closely related alkaloid, _neurin_. This transformation of a comparatively harmless alkaloid to an extremely deadly one simply by the partial decay of the plant in which the former is normally found, emphasizes very much the wisdom of rejecting for table use all specimens which are not entirely fresh. This advice applies to all kinds of mushrooms, and to worm-eaten and otherwise injured, as well as decayed ones. Neurin is almost identical in its physiological effects with muscarine, which is described below.

=Muscarine.=--This is the most important because the most dangerous alkaloid found in the mushrooms. It is most abundant in _Amanita muscaria_, it is also found in considerable quantity in _Amanita pantherina_, and to a lesser, but still very dangerous extent in _Boletus luridus_ and _Russula emetica_. It is quite probably identical with bulbosine, isolated from _Amanita phalloides_ by Boudier. _Muscarine_ is an extremely violent poison, .003 to .005 of a gram (.06 grain) being a very dangerous dose for a man. Like other constituents of mushrooms, the amount of muscarine present varies very greatly with varying conditions of soil and climate. This, indeed, may account for the fact that _Boletus luridus_ is regarded as an edible mushroom in certain parts of Europe, the environment being such that little or no muscarine is developed.

According to Kobert, _Amanita muscaria_ contains, besides choline and muscarine, a third alkaloid, _pilz-atropin_. This alkaloid, like ordinary atropin, neutralizes to a greater or less extent the muscarine. The amount of pilz-atropin present varies, as other constituents of mushrooms vary, with varying conditions of soil, climate, etc., and it may be that in those localities where the _Amanita muscaria_ is used for food the conditions are favorable for a large production of pilz-atropin which neutralizes the muscarine, thus making the plant harmless. Be this as it may, _Amanita muscaria_, so deadly as ordinarily found, is undoubtedly used quite largely as food in parts of France and Russia, and it has been eaten repeatedly in certain localities in this country without harm.

Fortunately muscarine has a very unpleasant taste. It is interesting in this connection to note that the _Amanita muscaria_ is said to be used by the inhabitants of Northern Russia--particularly the Koraks--as a means of inducing intoxication. To overcome the extremely unpleasant taste of the plant they swallow pieces of the dried cap without chewing them, or boil them in water and drink the decoction with other substances which disguise the taste.

The symptoms of poisoning with muscarine are not at once evident, as is the case with several of the less virulent poisons. They usually appear in from one-half to two hours. For the symptoms in detail we shall quote from Mr. V. K. Chestnut, Dept. of Agr., Washington (Circular No. 13, Div. of Bot.): "Vomiting and diarrhoea almost always occur, with a pronounced flow of saliva, suppression of the urine, and various cerebral phenomena beginning with giddiness, loss of confidence in one's ability to make ordinary movements, and derangements of vision. This is succeeded by stupor, cold sweats, and a very marked weakening of the heart's action. In case of rapid recovery the stupor is short and usually marked with mild delirium. In fatal cases the stupor continues from one to two or three days, and death at last ensues from the gradual weakening and final stoppage of the heart's action."

The treatment for poisoning by muscarine consists primarily in removing the unabsorbed portion of the mushroom from the alimentary canal and in counteracting the effect of muscarine on the heart. The action of this organ should be fortified at once by the subcutaneous injection, by a physician, of atropine in doses of from one one-hundredth to one-fiftieth of a grain. The strongest emetics, such as sulphate of zinc or apomorphine, should be used, though in case of profound stupor even these may not produce the desired action. Freshly ignited charcoal or two grains of a one per cent. alkaline solution of permanganate of potash may then be administered, in order, in the case of the former substance, to absorb the poison, or, in the case of the latter, to decompose it. This should be followed by oils or oleaginous purgatives, and the intestines should be cleaned and washed out with an enema of warm water and turpentine.

Experiments on animals poisoned by _Amanita muscaria_ and with pure muscarine show very clearly that when the heart has nearly ceased to beat it may be stimulated to strong action almost instantly by the use of atropine. Its use as thus demonstrated has been the means of saving numerous lives. We have in this alkaloid an almost perfect physiological antidote for muscarine, and therefore in such cases of poisoning its use should be pushed as heroically as the symptoms of the case will warrant. The presence of phallin in _Amanita muscaria_ is possible, and its symptoms should be looked for in the red color of the blood serum discharged from the intestines.

=Phallin.=--The exact chemical nature of this extremely toxic substance is not certainly known, but it is generally conceded to be of an albuminous nature. That it is an extremely deadly poison is shown by the fact that .0015 grain per 2 lbs. weight of the animal is a fatal dose for cats and dogs. It is the active principle of the most deadly of all mushrooms, the _Amanita phalloides_, or death-cup fungus. We quote again from Mr. Chestnut's account of phallin and its treatment: "The fundamental injury is not due, as in the case of muscarine, to a paralysis of the nerves controlling the action of the heart, but to a direct effect on the blood corpuscles. These are quickly dissolved by phallin, the blood serum escaping from the blood vessels into the alimentary canal, and the whole system being rapidly drained of its vitality. No bad taste warns the victim, nor do the preliminary symptoms begin until nine to fourteen hours after the poisonous mushrooms are eaten. There is then considerable abdominal pain and there may be cramps in the legs and other nervous phenomena, such as convulsions, and even lockjaw or other kinds of tetanic spasms. The pulse is weak, the abdominal pain is rapidly followed by nausea, vomiting, and extreme diarrhoea, the intestinal discharges assuming the 'rice-water' condition characteristic of cholera. The latter symptoms are persistently maintained, generally without loss of consciousness, until death ensues, which happens in from two to four days. There is no known antidote by which the effects of phallin can be counteracted. The undigested material, if not already vomited, should, however, be removed from the stomach and intestines by methods similar to those given for cases of poisoning by _Amanita muscaria_.

"After that the remainder of the poison, if the amount of phallin already taken up by the system is not too large, may wear itself out on the blood and the patient may recover. It is suggested that this wearing-out process may be assisted by transfusing into the veins blood freshly taken from some warm-blooded animal. The depletion of the blood serum might be remedied by similar transfusions of salt and warm water."

=Helvellic Acid.=--This very deadly poison is sometimes found in _Helvella esculenta_ Persoon (Gyromitra esculenta), particularly in old or decaying specimens. It has been studied and named by Boehm. It is quite soluble in hot water, and in some localities this species of _Helvella_ is always parboiled--the water being thrown away--before it is prepared for the table. It seems to be quite generally agreed that young and perfectly fresh specimens are free from the poison. As the poison is very violent, however, this plant should be carefully avoided.

The symptoms resemble in a very marked degree those of the deadly phallin, the dissolution of the red corpuscles of the blood being one of the most marked and most dangerous; this is accompanied by nausea, vomiting, jaundice, and stoppage of the kidneys. There is no known antidote for this poison, hence the little that can be done would be similar to that mentioned under phallin.

When poisoning by mushrooms is suspected, one cannot too strongly urge that the services of a competent physician should be secured with the least possible delay.