PHYSIOLOGY CHAP. 



ids,"siXch, for example, as the combinations of derivatives 

 of ammonia, in which the hydrogen of ammonia is combined 

 with other atomic groups. All these products of consumption 

 are of no further value for the life of the cells and tissues, and 

 are indeed harmful to them ; they must therefore be eliminated 

 in order that they may not disturb the normal functions. The 

 total losses thus sustained daily by the organism must be repaired 

 by fresh materials if life is to be maintained ; these materials 

 are represented by the food -stuffs and the oxygen, introduced 

 respectively by digestion and respiration. 



Hence a continual intake and output of material take place 

 in the organism, the intake being represented by the ingesta, 

 the output by the egesta or the excreta. Metabolism or exchange 

 of material comprises all the processes which bring about the 

 continuous change and renewal of material in the organism and 

 the study of the different conditions which modify them within 

 normal limits. 



Each cell, tissue, or organ has a metabolism of, its own. Since 

 they are all nourished and kept alive by the same nutritive 

 fluids, the blood and the lymph, it follows that the difference in 

 their products of assimilation and dissimilation is due to 

 the difference in their chemical, physical, and morphological 

 structure. 



The exact determination of the metabolism of the separate 

 tissues and organs is extremely difficult, because in the living 

 organism the amount of their exchange is more or less influenced 

 by all the others, at all events indirectly. The chemical processes, 

 which may be observed in excised organs which are kept alive 

 by means of an artificial circulation, enable us to study and 

 determine the specific qualities of their metabolism up to a 

 certain point, but do not give a physiological measurement. We 

 can, on the other hand, form a sufficiently close estimate of the 

 metabolism of the organism as a whole under different conditions 

 by comparing the quantity and quality of the intake with the 

 output, represented essentially by the urine, the faeces, and the 

 products discharged from the lungs and skin. 



In general metabolism the systems of both vegetative and 

 animal life take part. We shall see, indeed, that the nervous 

 system represents the supreme regulator of the exchange of both 

 material and energy. We are justified therefore in dealing with 

 this subject after discussing the two great systems in the life 

 of the higher animals and man. 



I. To Sanctorius (born 1561, died 1636) belongs the credit of 

 being the first to make experimental studies on general metabolism. 

 As a lecturer at Padua he published in 1614 a book entitled, 

 De medicina statica aphorismi, which contained the results of 

 many years of research upon the increase and decrease of the 



