556 GENERAL PHYSIOLOGY 



contradicting an old-established physiological dogma, is not so 

 wholly paradoxical as at first sight it appears. The dogma, which 

 has retarded not a little the advance of knowledge of vital 

 processes, and the origin of which is due simply to the fact that 

 investigators devoted themselves so exclusively to the vital 

 phenomena of higher animals, is expressed in the statement that 

 the excretion of nitrogen in the urine is an absolute measure of 

 the proteid-transformation in the body. Such an assumption is 

 quite unproven, at least in this form.^ It may be said with a certain 

 amount of justification that the nitrogen- excreted in the urine is 

 derived from the decomposition of proteids. But there is ab- 

 solutely no justification for maintaining, vice versa, that all the 

 nitrogen of the proteid transformed in the body appears in the 

 urine. The fact that all food-proteid beyond a certain quantity is 

 transformed in the body into groups of atoms, the nitrogen of 

 which is excreted in the urine, cannot be generalised, and especially 

 it cannot be applied to the decomposition of organised proteid, the 

 biogens. As is well known, both non-nitrogenous and nitrogenous 

 groups of atoms are derived from the decomposition of the biogen 

 molecule. The non-nitrogenous groups such as carbonic acid, 

 water, lactic acid, etc., leave the body at once. But the assumption 

 is not required that all the nitrogenous groups also leave the body 

 at once. It is conceivable that under certain circumstances the 

 nitrogenous residue becomes regenerated into a complete biogen 

 molecule at the expense of the food-stuffs and the oxygen, 

 or in hunger at the expense of the reserve-substances. There 

 would then be a decomposition of biogens which would result in 

 no excretion of nitrogen in the urine. There is no fact that 

 disputes the view that in muscle-activity the biogen molecule is 

 decomposed, and that, in general, the nitrogenous residue regener- 

 ates the lost non-nitrogenous groups of atoms at the expense of 

 the food. Such economy with the costly nitrogen would be wholly 

 in accord with the methods of the organic household. 



This idea, which has been here put forward simply as a possi- 

 bility suggested by the facts, upon more careful consideration 

 seems even probable. Before all else, it is in harmony with our 

 general physiological views upon the nature of the vital process, 

 and it accords with the ideas that must be formed, upon the basis 

 of innumerable facts, regarding the events occurring in living 

 substance. As is well known, the proteids are the chief constituents 

 of living substance, and they are also the sole organic substances 

 by the transformation of which alone the work of the living 

 organism can be maintained. Moreover, as has already been seen,^ 

 of all other substances that occur in the cell some serve for the 

 construction of the proteids and biogens, and some are derived from 

 the transformation of them. In other words, there can be no doubt 

 1 Of. p. 175. 2 Gf. pp. 163 and 479. 



