NITROGENOUS METABOLISM 157 



proteins and those of the various organs much as there are 

 between these same .blood-proteins and those of the food. 

 When a particular tissue, muscle, for example, is to be 

 nourished at the expense of the blood (or the lymph), a 

 true local digestion is necessary, and once more there must 

 be the selecting and rejecting of amino-acids. Those not 

 available may reach the liver and be deaminized there 

 quite as if they had come from the seat of the original 

 digestion. 



Note. The outlines of nitrogenous metabolism given 

 in this chapter follow closely Abderhalden's presentation 

 of the subject. It is impossible to predict how far the 

 prevailing views may be modified as the result of work now 

 in progress. Mendel's researches seem tending to support 

 the belief that more remodeling of the amino-acids can be 

 carried on than has been generally supposed. A recent 

 suggestion of his must be considered. The food which lies 

 in the intestine is not used solely by the animal, but serves 

 also to nourish swarms of bacteria. These are plants and 

 are known to possess well-marked synthetic powers. It is 

 certain that the multiplying bacteria construct new pro- 

 teins from the nitrogenous cleavage products placed at 

 their disposal. The proteins thus formed may be radically 

 different in molecular pattern from any in the diet. Great 

 numbers of these intestinal bacteria are always perishing, 

 and when they die they must yield their substance to the 

 digestive juices for resolution into its component groupings. 

 Thus there may be a hidden supply of amino-acids to the 

 system which is more or less independent of the ration 

 which the experimenter has furnished. 



Another possible divergence from the account given 

 above must be indicated. As we have pictured the suc- 

 cession of events, the amino-acids used for synthesis have 

 been combined to form the characteristic and abundant 

 proteins of the blood, these to be locally digested and made 

 to supply the necessary building units to the various 

 tissues. But the impression seems to be gaining in favor 



