292 SCIENCE OF AGRICULTURE. Part II. 



contains, besides the oil, gelatine, albumen, and other animal matters, which render it thick, dark- 

 coloured, and disposed to become rancid. Fish oil is sometimes extracted from the entire fish (as the 

 sprat, pilchard, and herring, when they occur in too great quantities to be salted), by boiling in water, 

 and skimming off the oil, as it appears on the surface. In general, however, the oil is obtained from the 

 livers of fish, in which it is lodged in cells. 



1953. The acids found in animals consist of various proportions of carbon, hydrogen, 

 oxygen, and azote. Some of them are peculiar to tlie animal kingdom, and others exist 

 in equal abundance in plants. * 



1954. The uric or lithic acid abounds in urine, and appears to be a production of the kidneys. The lactic 

 acid is common in the animal fluids. The amniotic acid has been found in the uterus of a cow. The 

 formic acid is procured by distilling ants. The benzoic, oxalic, acetic, and 7nalic acids are common both 

 to plants and animals, but seldom occur in the latter. 



1 955. These elements, by combining in different proportions, exhibit a great vai-iety 

 of separate substances. The earthy salts are likewise abundant ; and when they occur in 

 a separate state, they strengthen the albuminous fratnework, and form the skeleton, giving 

 stability to the body, and acting as levers to the muscles. The alkaline salts occur in the 

 greatest abundance in the secreted fluids. 



1956. The Jluids consist of those juices which are obtained from our food and drink, 

 such as the chyle, and are termed crude of the blood, or prepared from the crude fluids, and 

 destined to communicate to every part of the body the nourishment which it requires ; 

 and of those fluids which are separated from the blood, in the course of circulation, such 

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

 and are subject to motion and change. 



1957. The solids are derived from the fluids, and are usually divided into the soft and 

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

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

 grouped into faggots ; of plates, which, crossing one another in various directions, give 

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



1958. 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. 



1959. The cellular texture is universally distributed in the form of membranes, whicJi 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 whigh 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. 



1960. 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 homogenous, and its form is regulated by its 

 cellular envelope. 



1961. These soft solids alone are capable of possessing the faculty of sensation. By their aid, the nervous 

 energy is exerted on the different parts of the body ; and, through them, the impressions of external objects 

 are received. 



1962. 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. 



1963. The proportion between the solids and fluids is not only remarkably different in different species, 

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



Chap. IV. 



Animal Physiology ; the Digestive, Circulating^ and Reproductive Functions of Animals. 



Sect. I. Of the Digestive System. 



1964. 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. 



1 965. 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. 



1 966. Both hunger and thirst, besides being greatly influenced by habit, exhibit very 

 remarkable peculiarities, according to the species and tribes of animals, 



1 967. 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 

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



