Normal Fat Metabolism 



W. R. BLOCK 



BERKELEY 



Introductory 



In the course of the great development which has taken place in bio- 

 chemistry during the last few years our knowledge of metabolism has been 

 greatly extended, especially in the fields of the proteins and the carbo- 

 hydrates. Comparatively little has been added to that of the fats, for 

 which the main reason is the difficulty of chemical examination and de- 

 termination. The fats are relatively inert substances which do not lend 

 themselves readily to reactions which may be used as a basis for their 

 study, and as a result there is not the same background of exact chemical 



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knowledge as in the case of the proteins and carbohydrates. Another rea- 

 son is that in their function as stored material, the part which they and 

 their derivatives play in the life processes of the cells has been obscured, 

 and all the more so since the comparative inertness of the fats would seem 

 to render them unfit to take part in the delicately balanced reactions of 

 living protoplasm. Just the opposite may, however, be said of certain 

 of their derivatives such as the phospholipoids, members of which group 

 are among the most reactive substances found in living beings. In fact, 

 so great is their tendency to break up, to oxidize, to combine with a great 

 variety of substances that it is with extreme difficulty that they can be 

 prepared pure enough for analysis. In recent years methods have been 

 devised for the study not only of the fats but of the more important 

 related substances in living organisms, and the result has been an aroused 

 interest in the whole field. With the accumulation of data has come the 

 realization that the study of the metabolism of the fats, meaning essentially 

 that of the fatty acids, involves many if not all of the compounds of the 

 fatty acids, and that only by a consideration of the whole group of com- 

 pounds can a true picture of the metabolism of fat be obtained. For this 

 reason it has appeared necessary to reclassify the fats and related sub- 

 stances on the basis of their relationship to the fatty acids in metabolism, 

 and a brief outline of such a classification with a short description of 

 some of the more important members is given below. For a more detailed 



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