Part 13

Glauber’s salts and Epsom salts are other examples of solids which dissolve in water and separate in the crystalline form as the water evaporates; and which, like lime and gypsum, combine with a definite proportion of water to form crystalline compounds. In fact, each of these glassy brittle solids contains more than half its weight of water.

Thus we see that two bodies, of which water is one, may combine together to give rise to something different from either. And we are thus led to the science of =chemistry=, which tells us exactly how bodies combine, what comes of their combination, and how compounds may be separated into their constituents.

55. =Mineral bodies may take on definite shapes and grow, or increase in size, by the addition of like parts.=

Water and all the other natural bodies which have hitherto been mentioned, are what are called =mineral bodies=, although, in common use, the term mineral is usually restricted to ores and metals. Now we have repeatedly had occasion to remark that, under certain circumstances, not only water, but many other mineral bodies, assume regular shapes. The most familiar example is that of the beautiful imitation of leaves and foliage which is presented by the ice which forms on a window in winter. But we have also seen that common salt, lime, gypsum, Glauber’s salts and Epsom salts, also assume the crystalline form as they or their compounds with water are deposited from their solutions. And if a drop of solution of Glauber’s salts or of Saltpetre, is allowed to evaporate under the microscope, a wonderful spectacle will be presented. As the salt assumes the solid state, the crystals suddenly appear in the field of view as needles and plates disposed in beautiful patterns, which rival those of hoar frost, though they are quite different from them. In fact, as you will learn if you study =crystallography=, every crystallizable substance has its proper crystalline forms and never departs from certain strictly related geometrical figures.

A crystal of any of these substances will =grow= if placed under proper conditions. Thus, if a crystal of common salt is hung by a thread in a saturated solution of salt, which is exposed to the air, so as to allow the water to evaporate slowly, the molecules of the salt which is left behind and can no longer be held in solution, deposit themselves on the crystal in regular order and increase its size without changing its form. And, in this way, the small crystal may =grow= to a great size. The large crystals of sugar candy, which consist of sugar and water deposited from a strong syrup or saturated solution of sugar, grow in the same fashion, upon threads suspended in the evaporating syrup. In this mode of growth you will observe that the enlargement is effected by addition to the outside of the growing body; and moreover the matter which is added, namely, the salt or the sugar, already exists as salt in the brine or as sugar in the syrup.

B. LIVING BODIES.

56. =The Wheat Plant and the substances of which it is composed.=

Every one has seen a cornfield. If you pluck up one of the innumerable =wheat plants= which are fixed in the soil of the field, about harvest time, you will find that it consists of a stem which ends in a =root= at one end and an =ear= at the other, and that blades or =leaves= are attached to the sides of the stem. The ear contains a multitude of oval grains which are the =seeds= of the wheat plant. You know that when these seeds are cleared from the =husk= or =bran= in which they are enveloped, they are ground into fine powder in mills, and that this powder is the =flour= of which bread is made. If a handful of flour mixed with a little cold water is tied up in a coarse cloth bag, and the bag is then put in a large vessel of water and well kneaded with the hands, it will become pasty, while the water will become white. If this water is poured away into another vessel, and the kneading process continued with some fresh water, the same thing will happen. But if the operation is repeated the paste will become more and more sticky, while the water will be rendered less and less white, and at last will remain colourless. The sticky substance which is thus obtained by itself is called =gluten=; in commerce it is the substance known as =maccaroni=.

If the water in which the flour has thus been washed is allowed to stand for a few hours, a white sediment will be found at the bottom of the vessel, while the fluid above will be clear and may be poured off. This white sediment consists of minute grains of =starch=, each of which, examined with the microscope, will be found to have a concentrically laminated structure. If the fluid from which the starch was deposited is now boiled it will become turbid, just as white of egg diluted with water does when it is boiled, and eventually a whitish lumpy substance will collect at the bottom of the vessel. This substance is called =vegetable albumin=.

Besides the albumin, the gluten, and the starch, other substances, about which this rough method of analysis gives us no information, are contained in the wheat grain. For example, there is woody matter or =cellulose=, and a certain quantity of =sugar= and =fat=. It would be possible to obtain a substance similar to albumin, starch, saccharine and fatty matters, and cellulose, by treating the stem, leaves, and root in a similar fashion, but the cellulose would be in far larger proportion. =Straw=, in fact, which consists of the dry stem and leaves of the wheat plant, is almost wholly made up of cellulose. Besides this, however, it contains a certain proportion of mineral bodies, among them, pure flint or =silica=; and, if you should ever see a wheat rick burnt, you will find more or less of this silica, in a glassy condition, in the embers. In the living plant, all these bodies are combined with a large proportion of water, or are dissolved, or suspended in that fluid. The relative quantity of water is much greater in the stem and leaves than in the seed.

57. =The Common Fowl and the Substances of which it is Composed.=

Everybody has seen a common fowl. It is an active creature which runs about and sometimes flies. It has a body covered with feathers, provided with two wings and two legs, and ending at one end in a neck terminated by a head with a beak, between the two parts of which the mouth is placed. The hen lays =eggs=, each of which is enclosed in a hard shell. If you break an egg the contents flow out and are seen to consist of the colourless glairy “white” and the yellow “yolk.” If the white is collected by itself in water and then heated it becomes turbid, forming a white solid, very similar to the vegetable albumin, which is called =animal albumin=.

If the yolk is beaten up with water, no starch nor cellulose is obtained from it, but there will be plenty of fatty and some saccharine matter, besides substances more or less similar to albumin and gluten.

The feathers of the fowl are chiefly composed of horn; if they are stripped off and the body is boiled for a long time, the water will be found to contain a quantity of =gelatin=, which sets into a jelly as it cools; and the body will fall to pieces, the bones and the flesh separating from one another. The bones consist almost entirely of a substance which yields gelatin when it is boiled in water, impregnated with a large quantity of salts of lime, just as the wood of the wheat stem is impregnated with silica. The flesh, on the other hand, will contain albumin, and some other substances which are very similar to albumin, termed =fibrin= and =syntonin=.

In the living bird, all these bodies are united with a great quantity of water, or dissolved, or suspended in water; and it must be remembered that there are sundry other constituents of the fowl’s body and of the egg, which are left unmentioned, as of no present importance.

58. =Certain Constituents of the Body are very similar in the Wheat Plant and in the Fowl.=

The wheat plant contains neither horn, nor gelatin, and the fowl contains neither starch, nor cellulose; but the albumin of the plant is very similar to that of the animal, and the fibrin and syntonin of the animal are bodies closely allied to both albumin and gluten.

That there is a close likeness between all these bodies is obvious from the fact that when any of them is strongly heated, or allowed to putrefy, it gives off the same sort of disagreeable smell; and careful chemical analysis has shown that they are, in fact, all composed of the elements =Carbon=, =Hydrogen=, =Oxygen=, and =Nitrogen=, combined in very nearly the same proportions. Indeed, =charcoal=, which is impure carbon, might be obtained by strongly heating either a handful of corn, or a piece of fowl’s flesh, in a vessel from which the air is excluded so as to keep the corn or the flesh from burning. And if the vessel were a still, so that the products of this =destructive distillation=, as it is called, could be condensed and collected, we should find water and ammonia, in some shape or other, in the receiver. Now ammonia is a compound of the elementary bodies, nitrogen and hydrogen; therefore (§ 50) both nitrogen and hydrogen must have been contained in the bodies from which it is derived.

It is certain, then, that very similar nitrogenous compounds form a large part of the bodies of both the wheat plant and the fowl, and these bodies are called =proteids=.

59. =Proteid Substances are met with in Nature only in Animals and Plants; and Animals and Plants always contain Proteids.=

It is a very remarkable fact that not only are such substances as albumin, gluten, fibrin and syntonin, known exclusively as products of animal and vegetable bodies; but that every animal and every plant, at all periods of its existence, contains one or other of them, though, in other respects, the composition of living bodies may vary indefinitely. Thus, some plants contain neither starch nor cellulose, while these substances are found in some animals; while many animals contain no horny matter and no gelatin-yielding substance. So that the matter which appears to be the =essential= foundation of both the animal and the plant is the =proteid= united with =water=; though it is probable that, in all animals and plants, these are associated with more or less =fatty= and =amyloid= (or starchy and saccharine) substances, and with very small quantities of certain mineral bodies, of which the most important appear to be =phosphorus=, =iron=, =lime=, =and potash=.

Thus there is a substance composed of water + proteids + fat + amyloids + mineral matters which is found in all animals and plants; and, when these are alive, this substance is termed =protoplasm=.

60. =What is meant by the word Living?=

The wheat plant in the field is said to be a =living= thing; the fowl running about the farm-yard is also said to be a =living= thing. If the plant is plucked up, and if the fowl is knocked on the head, they soon die and become =dead= things. Both the fowl and the wheat plant, as we have seen, are composed of the same elements as those which enter into the composition of mineral matter, though united into compounds which do not exist in the mineral world. Why then do we distinguish this matter when it takes the shape of a wheat plant, or a fowl, as =living matter=?

61. =The Living Plant increases in size, by adding to the Substances which compose its Body, like Substances; these, however, are not derived from without, but are manufactured within the Body of the Plant from simpler Materials.=

In the spring, a wheat-field is covered with small green plants. These grow taller and taller until they attain many times the size which they had when they first appeared; and they produce the heads of flowers which eventually change into ears of corn.

In so far as this is a process of growth, accompanied by the assumption of a definite form, it might be compared with the growth of a crystal of salt in brine: but, on closer examination, it turns out to be something very different. For the crystal of salt grows by taking to itself the salt contained in the brine, which is added to its exterior; whereas the plant grows by addition to its interior: and there is not a trace of the characteristic compounds of the plant’s body, albumin, gluten, starch, or cellulose, or fat, in the soil, or in the water, or in the air.

Yet the plant creates nothing (§ 50) and, therefore, the matter of the proteids and amyloids and fats which it contains must be supplied to it, and simply manufactured, or combined in new fashions, in the body of the plant.