LECTURE XXVII. 



GENERAL METABOLISM. 



I. 



WE have so far considered for each foodstuff the way it is absorbed, 

 assimilated, and finally eliminated from the animal organism, and attempted, 

 above all else, to follow the intimate processes of metabolism in the tissues 

 and especially in the cells. The study of these processes separately has 

 to-day become the particular field of the physiological chemist. We should 

 err greatly, however, if we were to regard the chemical decompositions in 

 the animal organism solely from the standpoint of the individual food- 

 stuff. We should obtain an entirely false impression of the general meta- 

 bolism, and should be unable to answer some of the most important 

 questions. We have up to this time studied metabolism, as it were, from a 

 more or less qualitative standpoint. There remains the quantitative side 

 to be considered; i.e., we must compare the total income and the total outgo. 

 We have already touched upon this problem in discussing the transforma- 

 tion of the different organic foodstuffs into one another, and in considering 

 their mutual replacement according to their calorific value. 



It is particularly important for the study of metabolism that in the 

 economy of the animal organism the law of the conservation of matter 

 and of energy holds absolutely. This fact forms the basis of all experi- 

 ments in metabolism. We may determine, by studying as accurately 

 as possible the income and outgo, the part played by each individual 

 foodstuff in the general metabolism. Only by comparing the income 

 with the outgo are we able to form judgment as regards the condition of 

 the system. In this way alone is it possible to determine whether the 

 animal experimented upon increases its balance of nutrition, is in nutritive 

 equilibrium, or whether there is a deficit such that the organism is com- 

 pelled to draw upon its reserve stores or to consume its own tissue in order 

 to maintain the functions of its organs. The study of the body-weight 

 alone can never take the place of this important method of examination. 

 An increase or loss in weight may arise from a number of different causes. 

 Such deviations, for example, may be brought about merely by a retention 

 or an elimination of considerable water. The varied natures of the 

 problems concerning metabolism have led to different methods of investi- 

 gation. In some cases it is sufficient to follow the course of a single food- 



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