224 LECTURE XI. 



down in the same way as the proteins themselves, although they hardly 

 ever come into intimate contact with the cells. It has, moreover, never 

 been found possible to spare albumin by means of a mixture of amino 

 acids. The animal organism is evidently unable to build up its own 

 albumin from such material because other essential components are want- 

 ing. 1 Why should not groups result under normal conditions which are 

 unsuitable for further, synthesis and which are, therefore, immediately 

 deprived of the amino group and consumed ? 



The large albumin-requirement of the animal organism would be partly 

 explained by its constantly striving to obtain as much as possible of its 

 individual building-material. Here also the Law of the Minimum holds, 

 i.e. the extent of the syntheses taking place depends upon the amount of 

 that substance which is present relatively to the least extent. Again, 

 in the formation of the cell material from the serum-albumin, all of the 

 components of the latter are not utilized to the same extent. Under some 

 circumstances entire large groups may not be used at all. According to 

 this conception, it might be that a cell decomposition and replacement, 

 which of itself was not very extensive, might require a large amount of 

 proteins. But even with this assumption we are still unable to explain 

 the fact that a definite amount of albumin is necessary to maintain 

 an equilibrium in the metabolism. We would expect that the amount of 

 albumin used would be now more, now less. But the grown organism 

 maintains its metabolism in a very definite manner, and keeps it, with 

 very little variation, at a constant level. We ought to get a good idea of 

 all of these relations by exactly following the course of nitrogen metab- 

 olism of the salmon during its stay in fresh water. Remarkable trans- 

 formations occur in its organism. Its muscle- albumins finally produce 

 the protamines of entirely different composition. Are all of the elemen- 

 tary components of the former utilized? If this be so, then the animal 

 organism must be capable of converting one component into another. 

 These suggestions, needless to state, are insufficient to remove the haze 

 which still thickly envelops the whole metabolism of albumin. 



If we wish to consider this entire problem which is so important to 

 biology, we cannot neglect any single phase of the whole subject of the 

 transformation of material; and from this point of view it will be worth 

 our while to follow the utilization of the nutrient proteins and their value 

 in the animal organism. 



Although, in considering the questions concerning the assimilation of 

 the albumin from food, we met with great difficulties, these become appar- 

 ently unsurmountable when we attempt to follow the proteins till they 

 are taken up by the cells of the body. The enigmas begin with the 



1 E. Abderhalden and P. Rona: Z. physiol. Chem. 47 (1906) 



