ELEMENTS OF COMPOSITION. 27 



there exists a combination of butyric, caprinic, caprylic, and capronic 

 acids, with glycerin. 



According to the quantity of solid neutral fat dissolved in the triolein, 

 are the animal adipose tissues soft, or hard and suety after death. During 

 life, however, owing to the natural warmth of the body, they all remain 

 soft, and more or less fluid. In one and the same animal, moreover, the 

 adipose matter of many parts of the body may contain variable quantities 

 of solid fats. 



The neutral combinations of the latter occur widely distributed through- 

 out the body. They are to be met with in nearly all fluids and tissues 

 accompanying all the protein compounds and histogenic substances. 

 Their amount is very variable. They appear in enormous quantities in 

 the cells of fatty tissue, under the skin, in the orbit ; around the heart and 

 kidneys, and in bone; likewise in medullary nervous matter, together 

 with some special compounds, now better known than formerly. Its 

 constant presence in the tissues leaves no doubt as to the histogenic nature 

 of fat. On the other hand, other tissues 

 are frequently destroyed with fatty infil- 

 tration or generation, both physiological 

 and pathological (fatty degeneration). The 

 histogenic significance of the fats appears 

 greatly heightened when we remember the 

 fact that the hard crystalline combinations 

 forfeit their crystallizability on becoming 

 dissolved in triolein. 



Under certain circumstances, solid fat 

 separates from the natural fatty matters of 

 the body on the cooling of the latter after 

 death, in the form of needle-shaped crys- 

 tals Or groups Of the Same (fig. 3). These Fig. 3. Crystals of margarin. a, single 



are known to the microscopist as margarin 



crystals. a fat-cell quite free of them. 



REMARKS. The percentage of fats in different tissues is in lymph, 0'05 ; in chyle, 

 0-2 ; blood, 0'4; cartilage, 1'3 ; bone, 1-4 ; lens, 2'0 ; liver, 2'4 ; muscle, 3'3 ; brain, 

 8'0; nerves, 221; spinal cord, 23 '6; fatty tissue, 827; yellow marrow of bones, 

 96-0. 



19. 



In considering the objects for which fat is designed in the human 

 system, the following points may be borne in mind : 



1. The fats appear important, owing to their soft, fluid consistence 

 at the ordinary temperature of the living body, as distributors of pres- 

 sure, as pads and filling-up matters in various positions. 



2. Large collections of neutral fats, as bad conductors, prevent to a 

 certain extent loss of heat to the system. 



3. They possess the somewhat subordinate property of rendering 

 many hard tissues, such as epidermis and hair, pliant and soft, by satu- 

 rating them. For this purpose the secretions of the sebaceous glands 

 appear particularly designed. 



4. Their want of affinity for water seems to render them peculiarly 

 suited to separate from watery fluids in the form of granules and drops, 

 and so give origin to the formation of elementary molecules and vesicles. 



