ELEMENTS OF COMPOSITION. 25 



stomach and intestines, as a product of the fermentation of hydro- 

 carbons. 



( . C 4 H.O 

 With glycerin as tributyrin, = C 3 H 5 \ . C.H-0 it is a constituent 



( o.cXo 



of neutral butter fat. 

 Capronic, C 6 H 12 2 . Caprylic, C 8 H 16 2 . Caprinic, C 10 H SO O, . Acids. 



These are met with, in a free state, with glycerin, as constituents of 

 butter, and possibly also of sweat. 



Among the higher members of the group with which we are engaged, 

 there occur several of these acids (usually solid at the ordinary tempera- 

 ture of the body) as constituents of the neutral fats, and consequently 

 as histogenic compounds. They are introduced into the system with 

 the flits of the alimentary matters as a rule. Their physiological decom- 

 position probably results in the production of carbonic acid and water by 

 oxidation, at the same time that the series is split up into lower members. 



Palmitic Acid, C 16 H 82 3 . 



Palmitic acid is an element in almost all fats of the vegetable and ani- 

 mal kingdom. Its melting point is about 62 C. It crystallizes in glit- 

 tering pearly scales. 



This acid forms with glycerin a compound occurring naturally and 

 abundantly in human fat, as 



Tripalmitin, 



(O.C 16 H 81 

 C,H 5 O.C 16 H 31 0. 

 (O.C M H n O. 



Stearic Acid, C^H^O, . 



This is also a widely-spread constituent of the animal neutral fats, and 

 is present in the human body. Here, however, it is exceeded in quan- 

 tity by palmitic acid ; but it preponderates, on the other hand, in more 

 solid suety fats, as those of cows and sheep. Its melting point is higher 

 than that of the preceding acids, being about 69 C. It crystallises in 

 white silvery needles or scales. 



Its neutral combination with glycerin is known as 



O.C,H aK 



I8"35 V 



Tristearin, C 3 H 5 O . C, ^H, S O 



Among the acids of the second group there is only one of any import- 

 ance in the human economy, namely 



Oleic Acid (Elaidic Acid), C, 8 H 84 S . 



Pure oleic acid is met with as a fluid which stiffens into leaves at a 

 temperature of - 4 C. It is scentless and tasteless, and cannot be volati- 

 lised without decomposition. Its salts are not crystallizable. 



Elaidic acid is found as a most important constituent of the neutral 

 fats of the body, combined with glycerin, namely, as 



