2 PHYSIOLOGY CHAP. 



compounds, such, 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 

 m order that they may not disturb the normal functions The 

 total losses thus sustained daily by the organism must be repaired 

 by iresh 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 

 m the organism, the intake being represented by the ingesta 

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

 ot 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 



SSL^ M T" 1 ?^ and kept alive ^ the e nutritive 

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



their products of assimilation and dissimilation is due to 

 str e ucture renCe m chemi l, physical, and morphological 



The exact determination of the metabolism of the separate 

 tissues and organs is extremely difficult, because in the living 



bv^nT th ' amou f nt n f thelr eXGhan g e is more or le *s influenced 

 which L bf\ 'IT 611 ' 8 indir / ctl 7- The chemical processes, 

 which may be observed m excised organs which are kept alive 

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

 ceS'noi ^^T^ qUaUtie8 f their metabolism up to a 

 n on Cn^ K ^V 1 a P^ologfcal measurement. We 

 ntetabolSn of t?T hand ' form a efficiently close estimate of the 

 ibohsm 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 Tnd 

 products discharged from the lungs* and skin' 



animal ffttotS^L^ - d 



"' 





