784 ANATOMY OF VERTEBRATES. 



under conditions which vary in the degree of temperature re- 

 quired for congelation, as ' oil,' ' marrow,' ' lard,' ' spermaceti,' 

 * suet.' The most solid fats when subject to pressure afford 

 some fluid oil, termed ( elaine,' and when the fluid fats are cooled 

 to about 32 they deposit a concrete element called ( stearine : ' 

 the temperatures of congelation indicate the varying proportions 

 of elaine and stearine. Whether or not it be in relation to the 

 degree of cold to which the hoofs of some ruminants are subject, 



in traversing the snows of arctic climes, the oil called ' neat's 



~ 



foot ' owes its use in the arts to its maintaining its fluidity below 

 the freezing point. Blubber-oil, which becomes lardy at 45 or 

 50 Fahr., and is fluid above 55, most abounds in the thick 

 subcutaneous tissue of the Cetacea. The fat of the hog-tribe, 

 horse-tribe, most Lissencephala, Carnivora, Quadrumana, and 

 Birnana, is in the state of ' lard.' It exists as suet and tallow in 

 Ruminants. Spermaceti is peculiar to the Cachalot whales 

 (P/tyseter, Euphysetes). 



Some Rodents, the Hare, e.g., show little or no fat; but it 

 occasionally accumulates in the tame Rabbit. In many Rodents 

 it is limited to the abdominal cavity and its special peritoneal 

 processes. In the Seal-tribe and Whale-tribe, on the contrary, 

 there is no fat in the abdomen, or in the mesenteric or omental 

 duplicatures of the lining membrane. The subcutaneous areolar 

 tissue to which it is limited in these aquatic mammals has a 

 coarser reticulate structure in the Seals, the Grampus, and Bales- 

 ncptera, than in the Porpoise, Sperm-whale, and Balcena. In all 

 Cetacea the containing tissue is finer upon the trunk, and coarser 

 toward the tail. Fat is subcutaneous in the Hog and human sub- 

 ject, but is also present in the great serous cavities, intermuscular 

 spaces and joints, in variable degrees. 



Fat is to the adult what milk is to the young a source of 

 nourishment Avheii no other is available. Certain Bovines of the 

 tropics, where during the rainy season luxuriant grasses abound 

 on plains parched up in the dry season, accumulate fat and other 

 assimilable substances in a dorsal hump at the period of plenty, 

 and absorb its contents during that of drought. The Camels, 

 when their food abounds, store up similar superabundant nutritious 

 matters in one ( C. dromedarius) or two (C. bactrianus) larger 

 humps : whereby they are able to endure unusual fasts by re- 

 substance common to every class of matter.' xx. vol. iii. p. 209. The ternary com- 

 pounds of carbon, hydrogen, and oxygen, discovered in the condition of petroleum and 

 its allies, in mineral strata, are suspected, with good reason, to have originated in 



organic bodies. 



