642 LECTURE XXVII. 



the literature, as far as we are concerned it is an unknown quantity, and 

 at present we have practically no clear insight into cell-metabolism. For 

 the time being we recognize only the general stages of metabolism as a 

 whole. There is here a vast field for experimentation which has scarcely 

 been touched upon. It is only by a clear recognition of this fact that it 

 will be possible for us to penetrate fully unprejudiced into this obscurity, 

 and with new methods and new resources succeed in gradually developing 

 more and more facts which will replace the hypotheses. We have gone 

 into albumin metabolism upon a somewhat broad basis, because eventually 

 all questions concerning metabolism, no matter what their nature may be, 

 directly or indirectly penetrate into the problem of albumin metabolism 

 in the animal organism. The uncertainty which at present envelops the 

 latter to some extent affects all other investigations in this field, and 

 explains, at least to some extent, the different answers which have been 

 given the apparently similar questions concerning metabolism. 



In this connection we must once more remember that it is exceedingly 

 difficult to cause a deposition of albumin in the animal organism. Muscular 

 work has a remarkably favorable action in this direction. The significance 

 of work for accomplishing an albumin " fattening" has been recognized 

 by the physician. A retention of nitrogen has alone been satisfactorily 

 established in this connection. Less nitrogen appears in the urine than 

 the organism receives. We do not know what becomes of this nitrogen 

 that remains in the body. From the experiments of Schreuer 1 we know 

 that the "albumin" retained in the body is not equivalent to the remaining 

 albumin in the body. The deposited albumin is readily lost again, for when 

 the ordinary diet is resorted to, the organism soon returns to its usual 

 albumin condition. This is true especially of the nitrogen retention which 

 is brought about by a large supply of albumin. If, at the same time, 

 demands are placed upon a function of the body, e.g., that of the muscles, 

 we can easily imagine that the individual cells will attempt to utilize this 

 for increasing their cell material. 



In the fully developed organism there is also some occasion for albumin 

 being retained. It requires constructive material. Direct experiments 

 teach that the developed organism in fact constantly acquires nitrogen. 

 The adult organism during pregnancy finds itself placed under quite similar 

 conditions as during youth. Here again there is a constant formation of 

 new tissue to an unusual extent. Corresponding to this, P. Bar and R. 

 Daunay 2 showed that in the case of a gravid bitch, nitrogen was constantly 

 held back from the nourishment. This nitrogen retention was also notice- 

 able when the food was the same as that with which the animal was in 



1 Pfliiger's Arch. 110, 227 (1905). Cf. Karl Bornstein: ibid. 106, 66 (1904). 

 3 J. physiol. et pathol. g<n<ral, 1, 832 (1905). 



