ORGANIC FORMS OF THE ANIMAL BODY. 



organs for circulating their fluids, being the second characteristic peculiar 

 to animals. It is not so essential, however, as the digestive system, for it 

 is not found in the more simple species. 



The complicated functions of animals require organized systems, which 

 ■would be superfluous in vegetables ; such as, the muscular system for vo- 

 luntary motion, and the nerves for sensation. It was also necessary that 

 the fluids should be more numerous and varied in animals, and possessed 

 of a more complicated chemical composition than in plants, in order to 

 facilitate the action of these two systematic arrangements. Therefore, 

 another essential element was introduced into the composition of animals, 

 of which plants, excepting some few tribes, are generally deprived ; and 

 while plants usually contain only three elements, oxygen, hydrogen, and 

 carbon, animals add to these a fourth, namely, azote or nitrogen. This 

 difference in chemical composition forms the third trait in the character 

 of animals. 



Plants derive their nourishment from the soil and atmosphere, and thence 

 obtain water, composed of oxygen and hydrogen; also, carbonic acid, 

 which is a compound of carbon and oxygen ; while the atmosphere yields 

 an unlimited supply of air, composed of oxygen and nitrogen [with a slight 

 mixture of carbonic acid.] From these materials, the supplies necessary 

 to preserve their own composition unaltered, are obtained; and, while 

 hydrogen and carbon [with a certain portion of oxygen] are retained, 

 they exhale the superfluous oxygen [untainted.] The nitrogen, on the 

 contrary, is [either absorbed in very small quantities, or] altogether re- 

 jected. Such is the theory of vegetable composition ; in which one of 

 the most essential parts of the process, namely, the exhalation of oxygen, 

 can only be performed by the assistance of light. 



"When plants are deprived of ligHt, an opposite effect ensues. Instead of giving 

 off oxygen gas, and absorbing carbonic acid, the reverse takes place ; and carbonic acid 

 is disengaged, while oxygen is absorbed. The effect of plants upon the air is, there- 

 fore, to increase its purity during day-light, but to deteriorate its quality during the 

 darkness of night. 



Animals require for their nutriment, directly or indirectly, the same 

 substances which enter into the composition of vegetables, namely, hy- 

 drogen, carbon, [and a certain portion of oxygen.] But, in addition to 

 these, it is essential, for the preservation of their peculiar constitution, 

 that they accumulate a much larger portion of nitrogen, and disengage 

 any excess of hydrogen, and especially any superfluity of carbon. This 

 is performed by respiration, or breathing, in which process the oxygen 

 contained in the atmosphere combines with the [excess of] hydrogen 

 and carbon in the blood; with the former of these, it forms watery va- 

 pour, and with the latter carbonic acid. The nitrogen, to whatever part 

 of the system it may penetrate, seems chiefly (though not altogether) to 

 remain there. 



The quantity of nitrogen retained in the system varies with the seasons, being 

 greater in summer, and less in winter. The degree of variation is different for ani- 

 mals of different species; in some it is very small in quantity, while in others it is 

 equal to their entire bulk. 



The effects produced upon the atmosphere by plants and animals, are 

 of an opposite kind ; the former decompose water and carbonic acid, 

 while the latter reproduce them. Respiration forms the fourth character- 

 istic of animals, and is the most distinguishing function of the animal frame ; 

 namely, that which forms its essential diffi:;rence from all other beings, 

 and in a manner constitutes it an animal. So important is its influence 

 over the whole body, that we shall presently be able to show, that ani- 

 mals perform the functions of their nature with greater or less perfection, 

 according as their respiration is more or less perfect. 



Thus we perceive that animals are distinguished from plants by the following cha- 

 racteristics : — 1 st. They are possessed of an intestinal canal ; 2dly, Of a circulating 

 system; 3dly, Nitrogen enters largely into their composition; and finally. They are 

 endowed with organs adapted for respiration. 



SECT. IV. THE ORGANIC FORMS OF THE ANIMAL BODY, AND THE PRINCIPAL 



CHEMICAL ELEMENTS OF ITS COMPOSITION. 



Cellular Tissue — Membranes — Gelatine — Medullary Substance — Muscular Fibre — 

 Fibrin — Blood — Albumen — Secretion — Nutrition. 



A POROUS tissue of network, and at least three chemical elements (car- 

 bon, hydrogen, and oxygen), are essential to all living bodies, while a 

 fourth element (nitrogen) may be almost considered peculiar to animals. 

 We shall now proceed to describe the various kinds of meshes, of which 

 the network is composed, and the different combinations into which these 

 four elements are found to enter. 



There are three kinds of organized principles, or forms of network; 

 the cellular tissue, the medullary substance, or marrow, and the muscular 

 fibre. To each of these forms is attached a peculiar combination of che- 

 mical elements, as well as a particular function. 



The cellular substance is composed of an indefinite number of small 

 lamina2, without any apparent arrangement, crossing so as to form very 

 small cells, communicating with each other. It may be compared to a 

 species of sponge, similar in form to the entire body; while all other ani- 

 mal particles either occupy its cells, or traverse its substance. It pos- 

 sesses the property of contracting indefinitely when the causes, which 

 preserved it in a state of extension, are removed. Tliis power retains 

 the body within the limits, and in the form, assigned to it by Nature. 



The cellular substance, or tissue, enters into the composition of every part, forming 

 regular series of cells. We find it equally in the brain, the eye, and the nerves, only 

 somewhat finer in its texture than in the bones and muscles. Its ceUs move with fa- 

 cihty, and accommodate themselves to the motions of the body, being moistened, at the 

 points of contact with the adjacent cells, by a liquid, which lubricates them like the 

 synovia, or oily fluid of joints, so as to facihtate their motion. 



When the cellular substance is compressed into compact plates, it 

 forms laminae of various extent, called membranes. These membranes, 

 when united into cylindrical tubes, more or less ramified, receive the 

 name of vessels. The filaments, called fibres, are entirely composed of 

 cellular substance ; and the bones are nothing more than cellular substance, 

 rendered hard by the deposition of earthy particles. 



The general matter of which the cellular substance is composed, con- 

 sists in the proximate principle or combination, called gelatine; the dis- 

 tinguishing character of which is, that it can be dissolved by boiling water, 

 and, upon cooling, takes the form of a tremulous jelly. 



Gelatine, when analyzed by Gay-Lussac and Thenard, was found to contain in 100 

 parts, by weight — carbon, 48; hydrogen, 8; oxygen, 27; and nitrogen, 17; very 

 nearly. 



The 7nedullari/ substance cannot be resolved into any simpler organic 

 structure. It appears to the eye as a soft whitish pulpy matter, com- 

 posed of an infinite number of very minute globules. No peculiar mo- 

 tions can be observed in it ; but it possesses that most wonderful of all 

 properties, the power of transmitting to the mind the impressions made 

 on the external organs of sense, and of rendering the muscles subser- 

 vient to the determinations of the will. The brain and spinal marrow are 

 almost entirely composed of medullary substance ; and the nerves, which 

 are distributed through all the organs capable of sensation, are, in respect 

 to their composition, nothing but bundles (or fasciculi) of this substance. 



The muscular, or &eshy fibi-e, is composed of a particular kind of fila- 

 ments, having the peculiar property, during life, of contracting or folding 

 themselves up, when touched or injured by any external body ; or when 

 acted upon, through the medium of the nerves, by the will. 



The muscles are the immediate organs of voluntary motion, and are 

 composed entirely of bundles of fleshy fibres. All the membranes and 

 vessels, which are required to exercise any compressive force, are armed 

 with these fibres. They are always united intimately with the nervous 

 filaments, or threads ; but certain muscles are observed to execute mo- 

 tions, altogether independent of the wiU, especially in the exercise of func- 

 tions possessed in common with plants. Thus, although the will is fre- 

 quently the cause of muscular motion, yet its power is neither general 

 nor uniform in its action. 



Fleshy fibre has, for the basis of its composition, a particular principle, 

 named fibrin, which is [nearly] insoluble in boiling water, and seems na- 

 turally to assume a filamentous arrangement. 



It consists of white solid fibres, inodorous and insipid. When analysed by Gay- 

 Lussac and Thenard, 100 parts were found to contain about 53 parts of cai'bon, 7 of 

 hydrogen, 20 of oxygen, and 20 of nitrogen. 



The nutritive fluid, or blood, when recently extracted from the circulat- 

 ing vessels, may not only be ultimately resolved, for the most part, into the 

 general elements of the animal body, carbon, hydrogen, oxygen, and nitro- 

 gen ; but it already contains fibrin and gelatine, prepared to contract their 

 substance, and to assume respectively the forms of filaments or of mem- 

 branes, according to circumstances, whenever a slight repose enables them 

 to exhibit this tendency. In addition to these, the blood contains an- 

 other proximate principle, called albumen, [composed very nearly of 53 

 parts of carbon, 7 of hydrogen, 24 of oxygen, and 16 of nitrogen.] Its 

 character is to coagulate in boiling water, [like the white of eggs, com- 

 posed almost entirely of albumen.] We also find in the blood nearly all 

 the other elements, which enter into the composition of each animal body 

 in small quantities ; such as, the lime and phosphorus deposited in the 

 bones of the higher animals ; the iron, which seems essential to the colour 



