Читать книгу Scientific American Supplement, No. 275, April 9, 1881 - Various - Страница 6

To be intelligible, I must commence by some very brief remarks on the tissues of vegetables. There are two sorts distinguished among plants; some seem of no importance in the phenomena of nutrition; others, on the contrary, tend to the assimilation of the organic or inorganic components which should nourish and develop all the parts of the plant. The latter have a striking analogy with ferments; their composition is almost similar, and their action is increased or diminished by the same causes.

These tissues, formed in a state of repose in vegetables as in grain, have special properties; thus the berry possesses a pericarp whose tissues should remain foreign to the phenomena of germination, and these tissues show no particularity worthy of remark, but the coating of the embryo, which should play an active part, possesses, on the contrary, properties that may be compared to those of ferments. With regard to these ferments, I must further remark that I have not been able, nor am I yet able, to express in formula my opinion of the nature of these bodies, but little known as yet; I have only made use of the language mostly employed, without wishing to touch on questions raised by the effects of the presence, and by the more complex effects of living bodies, which exercise analogous actions.

With these reservations I shall proceed to examine the tissues in the berry which help toward the germination.

THE EMBRYO (10, see woodcut) is composed of the root of the plant, with which we have nothing to do here. This root of the plant which is to grow is embedded in a mass of cells full of fatty bodies. These bodies present this remarkable particularity, that they contain among their elements sulphur and phosphorus. When you dehydrate by alcohol 100 grammes of the embryo of wheat, obtained by the same means as the membrane (a process indicated later on), this embryo, treated with ether, produces 20 grammes of oils composed elementarily of hydrogen, oxygen, carbon, azote, sulphur, and phosphorus. This analysis, made according to the means indicated by M. Fremy, shows that the fatty bodies of the embryo are composed like those of the germ of an egg, like those of the brain and of the nervous system of animals. It is necessary for us to stop an instant at this fact: in the first place, because it proves that vegetables are designed to form the phosphoric as well as the nitrogenous and ternary aliments, and finally, because it indicates how important it is to mix the embryo and its dependents with the bread in the most complete manner possible, seeing that a large portion of these phosphoric bodies always become decomposed during the baking.

COATING OF THE EMBRYO.–This membrane (6), which is only an expansion of the embryo, surrounds the endosperm; it is composed of beautiful irregular cubic cells, diminishing according as they come nearer to the embryo. These cells are composed, first, of the insoluble cellular tissue; second, of phosphate of chalk and fatty phosphoric bodies; third, of soluble cerealine. In order to study the composition and the nature of this tissue, it must be completely isolated, and this result is obtained in the following manner.

The wheat should be damped with water containing 10 parts in 100 of alcoholized caustic soda; at the expiration of one hour the envelopes of the pericarp, and of the testa Nos. 2, 3, 4, 5, should be separated by friction in a coarse cloth, having been reduced by the action of the alkali to a pulpy state; each berry should then be opened separately to remove the portion of the envelope held in the fold of the crease, and then all the berries divided in two are put into three parts of water charged with one-hundredth of caustic potash. This liquid dissolves the gluten, divides the starch, and at the expiration of twenty-four hours the parts of the berries are kneaded between the fingers, collected in pure water, and washed until the water issues clear; these membranes with their embryos, which are often detached by this operation, are cast into water acidulated with one-hundredth of hydrochloric acid, and at the end of several hours they should be completely washed. The product obtained consists of beautiful white membranes, insoluble in alkalies and diluted acids, which show under the microscope beautiful cells joined in a tissue following the embryo, with which it has indeed a striking analogy in its properties and composition. This membrane, exhausted by the alcohol and ether, gives, by an elementary analysis, hydrogen, oxygen, carbon, and azote. Unfortunately, under the action of the tests this membrane has been killed, and it no longer possesses the special properties of active tissues. Among these properties three may be especially mentioned:

1st. Its resistance to water charged with a mineral salt, such as sea salt for instance

2d. Its action through its presence.

3d. Its action as a ferment.

The action of saltwater is explained as follows: When the berry is plunged into pure water it will be observed that the water penetrates in the course of a few hours to the very center of the endosperm, but if water charged or saturated with sea salt be used, it will be seen that the liquid immediately passes through the teguments Nos. 2, 3, 4, and 5, and stops abruptly before the embryo membrane No. 6, which will remain quite dry and brittle for several days, the berry remaining all the time in the water. Should the water penetrate further after several days, it can be ascertained that the entrance was gained through the part No 10 free of this tissue, and this notwithstanding the cells are full of fatty bodies. This membrane alone produces this action, for if the coatings Nos. 2, 3, 4, and 5 be removed, the resistance to the liquid remains the same, while if the whole, or a portion of it, be divided, either by friction between two millstones or by simple incisions, the liquid penetrates the berry within a few hours. This property is analogous to that of the radicules of roots, which take up the bodies most suitable for the nourishment of the plant. It proves, besides, that this membrane, like all those endowed with life, does not obey more the ordinary laws of permeability than those of chemical affinity, and this property can be turned to advantage in the preservation of grain in decortication and grinding.

To determine the action of this tissue through its presence, take 100 grammes of wheat, wash it and remove the first coating by decortication; then immerse it for several hours in lukewarm water, and dry afterwards in an ordinary temperature. It should then be reduced in a small coffee mill, the flour and middlings separated by sifting and the bran repassed through a machine that will crush it without breaking it; then dress it again, and repeat the operation six times at least. The bran now obtained is composed of the embryous membrane, a little flour adhering to it, and some traces of the teguments Nos. 2, 3, 4, and 5. This coarse tissue-weighs about 14 grammes, and to determine its action through its presence, place it in 200 grammes of water at a temperature of 86°; afterwards press it. The liquid that escapes contains chiefly the flour and cerealine. Filter this liquid, and put it in a test glass marked No. 1, which will serve to determine the action of the cerealine.

The bran should now be washed until the water issues pure, and until it shows no bluish color when iodized water and sulphuric acid are added; when the washing is finished the bran swollen by the water is placed under a press, and the liquid extracted is placed, after being filtered, in a test tube. This test tube serves to show that all cerealine has been removed from the blades of the tissue. Finally, these small blades of bran, washed and pressed, are cast, with 50 grammes of lukewarm water, into a test tube, marked No. 3; 100 grammes of diluted starch to one-tenth of dry starch are then added in each test tube, and they are put into a water bath at a temperature of 104° Fahrenheit, being stirred lightly every fifteen minutes. At the expiration of an hour, or at the most an hour and a half, No. 1 glass no longer contains any starch, as it has been converted into dextrine and glucose by the cerealine, and the iodized water only produces a purple color. No. 2 glass, with the same addition, produces a bluish color, and preserves the starch intact, which proves that the bran was well freed from the cerealine contained. No. 3 glass, like No. 1, shows a purple coloring, and the liquid only contains, in place of the starch, dextrine and glucose, i. e, the tissue has had the same action as the cerealine deprived of the tissue, and the cerealine as the tissue freed from cerealine. The same membrane rewashed can again transform the diluted starch several times. This action is due to the presence of the embryous membrane, for after four consecutive operations it still preserves its original weight. As regards the remains of the other segments, they have no influence on this phenomenon, for the coating Nos. 2, 3, 4, and 5, separated by the water and friction, have no action whatever on the diluted starch. Besides its action through its presence, which is immediate, the embryous membrane may also act as a ferment, active only after a development, varying in duration according to the conditions of temperature and the presence or absence of ferments in acting.

I make a distinction here as is seen, between the action through being present, and the action of real ferments, but it is not my intention to approve or disapprove of the different opinions expressed on this subject. I make use of these expressions only to explain more clearly the phenomena I have to speak of, for it is our duty to bear in mind that the real ferments only act after a longer or shorter period of development, while, on the other hand, the effects through presence are immediate.

I now return to the embryous membrane. Various causes increase or decrease the action of this tissue, but it may be said in general that all the agents that kill the embryous membrane will also kill the cerealine. This was the reason why I at first attributed the production of dark bread exclusively to the latter ferment, but it was easy to observe that during the baking, decompositions resulted at over 158° Fah., while the cerealine was still coagulated, and that bread containing bran, submitted to 212° of heat, became liquefied in water at 104°. It was now easy to determine that dark flours, from which the cerealine had been removed by repeated washings, still produced dark bread. It was at this time, in remembering my experiences with organic bodies, I determined the properties of the insoluble tissue, deprived of the soluble cerealine, with analogous properties, but distinguished not alone by its solid organization and state of insolubility, but also by its resistance to heat, which acts as on yeast. There exists, in reality, I repeat, a resemblance between the embryous membrane and the yeast; they have the same immediate composition; they are destroyed by the same poisons, deadened by the same temperatures, annihilated by the same agents, propagated in an analogous manner, and it might be said that the organic tissues endowed with life are only an agglomeration of fixed cells of ferments. At all events, when the blades of the embryous membrane, prepared as already stated, are exposed to a water bath at 212°, this tissue, in contact with the diluted starch, produces the same decomposition; the contact, however, should continue two or three hours in place of one. If, instead of placing these membranes in the water bath, they are enveloped in two pounds of dough, and this dough put in the oven, after the baking the washed membranes produce the same results, which especially proves that this membrane can support a temperature of 212° Fah. without disorganization. We shall refer to this property in speaking of the phenomena of panification.

CEREALINE.–The cells composing the embryous membrane contain, as already stated, the cerealine, but after the germination they contain cerealine and diastase, that is to say, a portion of the cerealine changed into diastase, with which it has the greatest analogy. It is known how difficult it is to isolate and study albuminous substances. The following is the method of obtaining and studying cerealine. Take the raw embryous membrane, prepared as stated, steep it for an hour in spirits of wine diluted with twice its volume of water, and renew this liquid several times until the dextrine, glucose, coloring matters, etc., have been completely removed. The membranes should now be pressed and cast into a quantity of water sufficient to make a fluid paste of them, squeeze out the mixture, filter the liquid obtained, and this liquid will contain the cerealine sufficiently pure to be studied in its effects. Its principal properties are: The liquid evaporated at a low temperature produces an amorphous, rough mass nearly colorless, and almost entirely soluble in distilled water; this solution coagulates between 158° and 167° Fah., and the coagulum is insoluble in acids and weak alkalies; the solution is precipitated by all diluted acids, by phosphoric acid at all the degrees of hydration, and even by a current of carbonic acid. All these precipitates redissolve with an excess of acid, sulphuric acid excepted. Concentrated sulphuric acid forms an insoluble downy white precipitate, and the concentrated vegetable acids, with the exception of tannic acid, do not determine any precipitate. Cerealine coagulated by an acid redissolves in an excess of the same acid, but it has become dead and has no more action on the starch. The alkalies do not form any precipitate, but they kill the cerealine as if it had been precipitated The neutral rennet does not make any precipitate in a solution of cerealine–5 centigrammes of dry cerealine transform in twenty-five minutes 10 grammes of starch, reduced to a paste by 100 grammes of water at 113° Fah. It will be seen that cerealine has a grand analogy with albumen and legumine, but it is distinguished from them by the action of the rennet, of the heat of acids, alcohol, and above all by its property of transforming the starch into glucose and dextrine.

It may be said that some albuminous substances have this property, but it must be borne in mind that these bodies, like gluten, for example, only possess it after the commencement of the decomposition. The albuminous matter approaching nearest to cerealine is the diastase, for it is only a transformation of the cerealine during the germination, the proof of which may be had in analyzing the embryous membrane, which shows more diastase and less cerealine in proportion to the advancement of the germination: it differs, however, from the diastase by the action of heat, alcohol, etc. It is seen that in every case the cerealine and the embryous membrane act together, and in an analogous manner; we shall shortly examine their effects on the digestion and in the phenomena of panification.

PHOSPHATE OF CALCIUM.–Mr. Payen was the first to make the observation that the greatest amount of phosphate of chalk is found in the teguments adjoining the farinaceous or floury mass. This observation is important from two points of view; in the first place, it shows us that this mineral aliment, necessary to the life of animals, is rejected from ordinary bread; and in the next place, it brings a new proof that phosphate of chalk is found, and ought to be found, in everyplace where there are membranes susceptible of exercising vital functions among animals as well as vegetables.

Phosphate of chalk is not in reality (as I wished to prove in another work) a plastic matter suitable for forming bones, for the bones of infants are three times more solid than those of old men, which contain three times as much of it. The quantity of phosphate of chalk necessary to the constitution of animals is in proportion to the temperature of those animals, and often in the inverse ratio of the weight of their bones, for vegetables, although they have no bones, require phosphate of chalk. This is because this salt is the natural stimulant of living membranes, and the bony tissue is only a depot of phosphate of chalk, analogous to the adipose tissue, the fat of which is absorbed when the alimentation coming from the exterior becomes insufficient. Now, as we know all the parts constituting the berry of wheat, it will be easy to explain the phenomena of panification, and to conclude from the present moment that it is not indifferent to reject from the bread this embryous membrane where the agents of digestion are found, viz., the phosphoric bodies and the phosphate of chalk.