Book II. DIGESTIVE AND CIRCULATING SYSTEMS. 291 



as the bile, and termed secreted fluids. These are all contained in appropriate vessels, 

 and are subject to motion and change. 



1920. The solids are derived from the fluids, and are usually divided into the soft and 

 hard. The soft solids consist chiefly of whsA is termed animal matter, of combinations 

 of carbon, hydrogen, oxygen, and azote. They consist of fibres, which are usually 

 grouped into faggots ; of plates, vv^hich, crossing one another in various directions, give 

 rise to cellular structure, or of a uniform pulpy mass. 



1921. The fibrous texture may be observed in all the muscles, tendons, and ligaments, and in the bones 

 of many animals, especially before birth. These fibres, however minutely divided, do not appear to be 

 hollow, like those of the vegetable kingdom. 



1922. The cellular texture is universally distributed in the form'of membranes, which invest every 

 organ, the bundles of fibres in every muscle, and, by forming tubes with the addition of the fibrous 

 texture, constitute the containing vessels. The substance gives form to all the different parts, and is 

 that particular portion which is first formed, and which constitutes the frame on and within which the 

 other materials of the system are deposited. It readily expands by the increase of its contents; and, 

 with equal ease, contracts when the distending cause is removed. 



19-23. The pulpy texture is confined to the brain and nerves, the liver, kidneys, and other secreting 

 organs of the system. Its composition appears to the eye homogeneous, and its form is regulated by its 

 cellular envelope. 



1924. T/iese soft solids are alone capable of possessing the faculty of sensation. By their aid, the nervous 

 energy is exerted on the different parts of the body ; ^nd, through them, the impressions of external 

 objects are received. 



1925. The hard solids consist either of cartilage, which resembles, in its qualities, coagulated albumen; 

 or of bone, formed by various combinations of earthy salts. They are destitute of sensation, and are 

 chiefly employed in defending the system from injury, giving it the requisite stability, and assisting the 

 muscles in the execution of their movements. 



1926. The proportion between the solids and fluids is not only remarkably different in different specie*, 

 but in the same species, in the various stages of growth. 



Chap, IV. 

 Animal Physiology. 



1927. The digestive circulation and rejrroductive functions of animals come next in order. 



Sect. I. Of the Digestive System. 



1928. The instinct of animals for food, presides over the organs of the stomach. 

 Hunger is felt when the stomach is empty ; it is promoted by exercise, cold air applied 

 to the skin, and cold, acid, or astringent fluids introduced into the stomach. Inactivity, 

 warm covering, the attention diverted, and warm fluids, have a tendency to allay 

 the sensation. 



1929. Thirst is accompanied with a sensation of dryness in the mouth. This dryness 

 may be occasioned by excessive expenditure of the fluids, in consequence of the dryness 

 or saltness of the food which has been swallowed; or to their deficiency, from the state 

 of the organs. 



1930. Both hunger jand thirst, besides being greatly influenced by habit, exhibit very 

 remarkable peculiarities according to the species and tribes of animals. 



1931. Those which live on the spoils of the animal kingdom are said to be carnivorous, 

 when they feed on flesh ; piscivorous, when they subsist on fishes ; and insectivorous, 

 when they prey on insects. Again those animals which are phytivorous, or subsist 

 on the products of the vegetable kingdom, are either granivorous and feed on seeds ; 

 graminivorous, pasturing on grass ; or herbivorous, browsing on twigs and shrubs. 



1932. Besides those substances which animals make use of as food, water is likewise employed as drink, 

 and as the vehicle of nutritious matter. Salt is necessarily mixed with the drink of the inhabitants of 

 the ocean, and is relished by man and many other animals. Other inorganic substances are likewise 

 employed for a variety of purposes. Many savages make use of steatite and clay along with their food. 

 The common earthworm swallows the soil, from which, in its passage through the intestines, it extracts 

 its nourishment. ' 



1933. In some cases, substances are swallowed for other purposes than nourishment. Stones are retained 

 in the stomach of birds to assist in triturating the grain. The wolf is said to satisfy his hunger, by filling 

 his stomach with mud. 



Sect. II. Of the Circulating System. 

 1934. The food being reduced to a jyultaceous mass, and mixed with a variety of secreted 

 fluids, by means of the digestive organs, is in this state denominated chyme. This mix- 

 ture exhibits a chemical constitution nearly approaching that of blood, into which it is 

 destined to be converted, by the separation of the useless from the useful part. This is 

 effected by certain vessels called lacteals, which absorb the nutritious part of the chyme, 

 and convey it to a particular receptacle. Another set of absorbents, the lymphatics, 

 take up all the substances which have been ejected from the circulation, and which are 

 no longer necessary in the particular organs, and communicate their contents to the store 

 already provided by the lacteals. The veins receive the altered blood from the extremi- 

 ties of the arteries or the glands, in which they terminate, and proceed with it towards 



U 2 



