186 
HISTOLOGY OF ANIMALS. 
observed that the bones of the extremities are greasy 
at their distal ends, because the contents of the adipose 
cells are always of a liquid nature, and have little or no 
tissue to support them. 
According to chemists, fat consists of a liquid and 
solid principle, the former being termed elaine, the 
latter margarine ; in all the firmer fats, such as lard, a 
third principle, termed stearine, is also present. When 
speaking of oil in vegetables, I noticed the analogy 
between the fatty substances derived from plants and 
animals, and I mentioned that a stearine had for some 
time been procured from palm-oil, either by distillation, 
or by subjecting it to great pressure. Stearine may be 
obtained from human fat, and cannot readily be distin- 
guished from that of vegetable origin. 
It is generally known that the elaine and stearine of 
the fats, are compounds of the oleic and stearic acids, 
with a base termed glycerine, a substance now frequently 
employed in medicine, and also in mounting micro- 
scopical objects. This material is extensively obtained 
in the manufacture of soap. When oils or fats are 
boiled with caustic alkali, the compounds of stearic, oleic 
and margaric acids with glycerine, are decomposed, the 
former combining with the alkali, while the latter is set 
free, and is found in the soap-lees ; from which it is 
separated by a chemical process. The purest glycerine, 
which is almost colourless, is obtained in the manufac- 
ture of lead plaster. In this process, oil, litharge 
(oxide of lead) and water are boiled together, the oxide 
