Organic Substances and Formations. 299 



passes them away in secretions, or lays them down with his 

 bones to rest in their mother earth, fresh plants catch them up 

 again, and bring: them once more within the circle of organic 

 life. m * 



The simplest animals are composed wholly or chiefly of 

 sarcode, the soft stuff of which the infusoria are made, and 

 which with a little modification constitutes the bodies of the 

 polyps. As it occurs so commonly as a chief constituent of 

 the lower kinds of animals in their adult form, it is not sur- 

 prising that it is found in the larval or embryonic stages of 

 higher ones, including man himself. One of the best ways of 

 getting a notion of the appearance and properties of sarcode 

 is to look at an amoeba through a microscope. Chemically it 

 has a close relation to the muscular tissues of higher animals, 

 as it belongs to the proteic, or albumenoid group of bodies. 

 The principal substances composing albumen, the type of this 

 group, are, carbon, hydrogen, oxygon, and nitrogen, but small 

 quantities of sulphur, and some saline ingredients are always 

 present. Albumen is easily studied in its well-known form, 

 white of eg*g. Albumen, and its near relative fibrin, can exist 

 in two conditions, soluble and insoluble. The white of egg 

 readily coagulates on the application of heat, and fibrin, which 

 the blood holds in solution coagulates on being withdrawn 

 from the vessels of a living animal. Substances closely re- 

 sembling, or identical with albumen and fibrin, exist in the 

 vegetable world, and especially in seeds, which are found useful 

 for food. The albumenoid group are essential to animal life, 

 and probably to organic life, though their quantity in many 

 plants may be infinitesimal, and they are remarkable for the 

 facility with which they undergo chemical changes. They give 

 its chief nutritive value to milk, to the meal of peas, beans, 

 and other bodies standing high as food. 



As the object of the present paper is solely to help be- 

 ginners and those who are not special students of chemistry, 

 we shall not introduce any of the complicated questions relating 

 to the chemistry of the constituents of animal bodies, but add 

 a few words on some important compounds, beginning with 

 muscular tissue. It consists chiefly of coagulated fibrin, iC but 

 being highly vascular, and containing nearly three-fourths of 

 its weight of water, it is permeated with a fluid consisting 

 partly of blood and partly of substances secreted from it, 

 independently of a small portion of nervous and adipose 

 matter."* 



The portion of muscle which is soluble in cold water con- 

 sists of albumen, salts of the blood, and two crystallizable 

 animal principles named Jcreatine and inosite, several acids, and 

 * Prof. Miller's Elements C.'iem. 



