Chemical Constituents of the Animal Body. 183 



the extract is weighed, a rough quantitative approximation 

 to the fat content of the tissue can be made. The extrac- 

 tion is carried out generally in a Soxhlet extractor 

 (Fig. 23), which acts continuously. The powder 

 is introduced into a thimble made from fat-free 

 blotting paper which is introduced into a receptacle 

 which fits into a cork, or is ground into a wide- 

 mouthed flask containing the solvent. The upper 

 part of the receptacle is fitted to a reflux con- 

 denser, and it is also provided with two side tubes, 

 one of which is made in the form of a siphon. 

 The solvent is boiled, and passes up the one side 

 tube, is condensed in the condenser, and then 

 flows back into the thimble receptacle, until the 

 latter is filled up to the top of the siphon tube ; 

 when the solvent reaches this point, it siphons 

 back into the boiling flask. In this way the 

 substance is repeatedly extracted with fresh sol- 

 vent, only a limited amount of which is necessary 

 for a complete extraction. 



The Methods of characterizing Fats. Fats Fig 2 s. 

 from various sources differ from one another, as 

 already stated, in the fact that they yield different acids 

 on hydrolysis. These acids may be subdivided into various 

 classes according to their degree of saturation. The 

 following is a list of the chief acids which have been 

 obtained by the hydrolysis of fats : 



A. The saturated acids of the general formula C rt H 2n 02 



C. 2 H 4 O a V v , . . Acetic acid. 

 C 4 H 8 2 .... Butyric 



which are soluble in organic solvents are not readily extracted directly owing 

 to the formation of complexes with other constituents of the tissues. Various 

 methods have been suggested by Liebermann, Kumagawa, and Suto and others 

 for the quantitative estimation of fats in tissues ; for these reference must be 

 made to larger text-books. 



