Chemical Changes in Animal Organism. 267 



lished more than ten volumes during the course of the 

 year 1913. 



Within the scope of this book it is only possible to 

 deal with certain typical methods which have been employed 

 in research ; the results are discussed in detail more suit- 

 ably in works treating specially certain defined aspects of 

 physiology and pathology. 



In the present chapter it is proposed to deal with the 

 methods employed for the investigation of the chemical 

 changes of substances which take place within the mam- 

 malian body, and various reasons can be advanced for 

 choosing this subject first for special treatment. The chief 

 of these is the fact that the higher animals employ as the 

 chief sources of their food supply complex substances in- 

 cluded in three classes namely, the fats, the carbohydrates, 

 and the proteins. These substances undergo degradation 

 and oxidation in the organism, supplying thereby the 

 energy needs for muscular work and the heat requisite for 

 maintaining the body temperature above that of the sur- 

 roundings. They supply, in addition, the material neces- 

 sary to replace the tissue waste, and in the case of the 

 young growing organism, the substances necessary for the 

 manufacture of new tissues. The changes to be investi- 

 gated in the mammalian body are mainly of a degradative 

 character, as far more material is employed for energy 

 needs than is utilized for tissue growth and repair. Now 

 a degradation of a substance into simpler products is as 

 a rule easier to follow by experimental methods than is the 

 reverse process of a synthesis. It is, therefore, not sur- 

 prising that far more is known of the methods by means 

 of which foodstuffs are broken down and utilized than is 

 known of the methods by means of which new tissues are 

 built up. The mammalian organism, in which the degrada- 

 tive chemical changes far surpass in quantity those of a 



