FATS. 61 



their combinations, but they exist in minute quantity, and 

 their function is comparatively unimportant. 



Composition and Properties. In their ultimate composi- 

 tion, fats bear a certain resemblance to the sugars. Like 

 them they are composed of carbon, hydrogen, and oxygen ; 

 but the two latter elements do not exist, as in sugar, in the 

 proportions to form water. From this difference we should 

 be led to suspect, what is really the fact, that the different 

 varieties of fat are not mutually convertible. 



The fat which exists in the body is a mixture of the three 

 varieties above mentioned, and is found in the ordinary adi- 

 pose tissue, and in the substance of certain tissues in the 

 form of minute globules or granules. It is not found in any 

 great quantity in the blood, except after digestion of a full 

 meal. It exists in the chyle in a state of extremely minute 

 subdivision and suspension. It exists in the milk, also in a 

 state of minute subdivision, but presenting some slight differ- 

 ences from the ordinary fatty matter of the economy. 



Eobin and Yerdeil give, as the ultimate composition of 

 Stearine, C 71 H 70 O 8 . The other varieties are separated from 

 their union with each other with great difficulty, and have 

 not yet been obtained in a state of sufficient purity for ulti- 

 mate analysis. The reaction of all the varieties of fat is 

 neutral. 



Fat, in greater or less quantity, is found in all the tissues 

 of the body, with the exception of the substance of the bones, 

 the teeth, and the elastic and inelastic fibrous tissue. It 

 always consists of a mixture of the three varieties in varying 

 proportions, but, with one or two exceptions, is never com- 

 bined with any other of the proximate principles. In the 

 adipose tissue proper, it is enclosed in little cells which are 

 called the adipose vesicles. In all other situations it is in the 

 form of microscopic globules or granules. As it is thus dis- 

 tinct from other elements, it may be always recognized in the 

 organism by the naked eye or the microscope. In the ner- 



