588 OF FAT, AND OF WHAT BONES CONSIST. 



a kind of varnish when exposed to the air. Tliese latter facts are not 

 without their importance, as we shall hereafter see. 



The solid part of the fat of animals is known to vary to a certain ex- 

 tent among different races. Thus the solid fat of man is the same with 

 that of the goose, and with that which exists in olive oil and in butter. 

 To this the name of margarine is given. But the solid fat of the cow, 

 tffe sheep, the horse, and the pig, differs from that of man, and is 

 known by the name of stearine. 



The solid and fluid parts are mixed together in different proportions in 

 the fat, not only of different animals, but of the same animal at differ- 

 ent periods, and in different parts of its body. Hence the greater hard- 

 ness observed in the suet than in other portions of the fat of beef and mut- 

 ton, and hence also the different quality and appearance of the fat of an 

 ox according to the kind of food upon which it has been fed or fattened. 



c. T'he hones, Uke the muscles, consist of a combustible and an incom- 

 bustible portion, but in the bones the inorganic or incombustible part is 

 by much the greater. To the organic matter of bones the name of gel- 

 atine or glue is given, and it can be partly extracted from them by boil- 

 ing. The proportion of gelatine which exists in bones varies with the 

 kind of animal — widi ihe part of the body from which the bone is taken 

 — and very often with the age and state of health of the animal, and with 

 the way in which it has been accustomed to be fed. It is greater in spongy 

 bones, in the bones of young animals, and probably also in the bones of 

 such as are in high condition. In perfectly dry bone it rarely exceeds 

 from 35 to 40 per cent, of the whole weight. 



The incombustible portion consists for the most part of phosphate and 

 carbonate of lime. The relative proportions of these two earthy com- 

 pounds also vary with the kind of animal, with its age, its condition, its 

 food, and its state of health. To form 100 lbs. of bone the animal will 

 usually require to incorporate with its own substance about — 

 35 pounds of gelatine, 

 55 pounds of phosphate of lime, 

 4 pounds of carbonate of lime, 

 3 pounds of phosphate of magnesia, 

 3 pounds of soda, potash, and common salt. 



100 



d. Hair, horn, and wool, are distinguished from the muscular parts of 

 the animal body by the large proportion — about five per cent. — of sul- 

 phur which they contain. They consist of a substance which in other 

 respects closely resembles gluten and gelatine in its chemical composi- 

 tion (page 445). When burned, they leave from one to two per cent, of 

 ash, which in the case of a variety of human hair, which left 1-1 per cent, 

 of ash, was fimnd by Van Laer to consist of — 



Per cent. 



Soluble chlorides and sulphates 0-51 



Oxide of iron 0-39 



Phosphate and sulphate of lime, phosphate of magnesia and silica . 0-20 



1-10 

 The inorganic matter contained in l.air is therefore, generally speak- 



