February 27, 1885.] 



SCIENCE. 



173 



versy among physiologists; one school maintaining, 

 and another denying, that it is to be interpreted as 

 showing an excretion of gaseous nitrogen. 



There is one fact which renders the results ob- 

 tained by the experimental method just mentioned 

 inconclusive either for or against an excretion of 

 free nitrogen : it is that the animal experimented" 

 upon may either gain or lose nitrogenous matter from 

 the tissues of its body during the experiment. If 

 the former take place, the excretion of nitrogen is 

 diminished by that amount: if the latter happen, it 

 is increased. But, while such gain or loss of nitro- 

 genous matter by the body may undoubtedly take 

 place, we have no means of proving that a small 

 gain or loss has or has not occurred in any given 

 experiment. If in some trial the nitrogen of the 

 excreta exactly equal that of the food, the advocate 

 of the excretion of gaseous nitrogen can say that a 

 certain (unknown) amount of nitrogen may have 

 been lost from the body of the animal, and, by 

 chance, the same amount may have been excreted as 

 gas. If an experiment show a deficiency of nitrogen 

 in the excreta, the denier of the excretion of free 

 nitrogen can say that exactly that amount of nitrogen 

 may have been gained by the animal. Plainly, 

 neither of these possibilities can be either proved or 

 disproved by this method of experiment. 



A resort to an investigation of the respiratory 

 products naturally suggests itself. The experiment, 

 though a difficult one, has been made; but the re- 

 sults have not, as might have been hoped, sufficed to 

 decide the question definitely. 



It should be remembered that the amount of 

 nitrogen excreted as gas must, in any case, be small. 

 The large deficit found by the earlier experimenters 

 is universally acknowledged to have been erroneous. 

 Bearing this in mind, it is evident, that, as already 

 pointed out, a single experiment by the first method 

 has comparatively little weight. But very many such 

 experiments have been made, and, when properly 

 made (i.e., on mature animals, with food just suffi- 

 cient to maintain them without gain or loss of 

 weight), they all agree in showing a very small differ- 

 ence between the nitrogen of the food and that of the 

 excreta; and, moreover, the difference is sometimes 

 in one direction, and sometimes in the other. For 

 example : out of forty-three experiments by various 

 observers, whose results chance to lie before me, 

 nineteen show an excess of nitrogen in the excreta, 

 and twenty-four a deficiency, as compared with the 

 nitrogen of the food. The excess varies from 0.07% 

 to 6% of the total nitrogen fed; and the deficiency 

 from 0.02 % to 6.7 %. Many more observations might 

 he quoted to the same effect. Such results as these 

 have a cumulative force, and go far to establish the 

 hypothesis that there is no excretion of gaseous nitro- 

 gen. 



Some of the believers in an excretion of gaseous 

 nitrogen, particularly Seegen and Norwak in Vienna, 

 have attacked these results upon the side of the ana- 

 lytical methods employed, claiming that the process 

 (soda-lime process) used for estimating nitrogen 

 gives too low results. It has been shown, however, 



by several chemists, that this is not the case when 

 the process is properly performed; while some recent 

 trials by Gruber 1 show, that, when the so-called 

 'absolute method' for nitrogen is employed, substan- 

 tially the same results are reached. 



The main reliance of those who believe that ani- 

 mals excrete free nitrogen, however, is upon respira- 

 tion experiments, nearly all of which appear to favor 

 their view. These experiments are made substan- 

 tially in the following manner. The animal breathes 

 in a confined volume of air of known amount, whose 

 exact composition is determined by analysis before 

 the experiment begins. As the oxygen of the con- 

 fined air becomes exhausted, measured quantities of 

 pure oxygen are admitted from a gas-holder, while 

 the carbonic acid which is exhaled is absorbed by 

 caustic potash. At the close of the experiment the 

 air in the apparatus is again analyzed ; and the ob- 

 server then proceeds to compute, from the data he 

 has secured, the amount of nitrogen originally pres- 

 ent in the air within the apparatus, and the amount 

 remaining at the close of the experiment. If the 

 latter quantity is found to be the larger, it shows 

 (barring experimental errors) that the animal has 

 exhaled gaseous nitrogen. # 



Almost, if not quite, every experiment made on this 

 plan has shown an apparent small excretion of free 

 nitrogen. Thus the well-known experiments of 

 Kegnault and Beiset appear to show an excretion 

 of free nitrogen by various animals. In their experi- 

 ments with small animals the amount was relatively 

 small; and sometimes an absorption of nitrogen was 

 observed, especially during hunger. In experiments 

 with larger animals (sheep and calves), in a larger 

 apparatus, the apparent excretion was quite consider- 

 able. 



Seegen and Norwak in Vienna have reported nu- 

 merous trials with a simplified form of Begnault and 

 Beiset' s apparatus, all of which show an apparent 

 excretion of nitrogen ; and a lively debate has been 

 carried on between them and Voit, each party endeav- 

 oring to explain away the results of the other. 



Some recent experiments by Leo 2 are of much in- 

 terest in this connection. He worked with rabbits, 

 which were tracheotomized and supplied with pure 

 oxygen. After sufficient time had elapsed to remove 

 all free nitrogen from the lungs, the expired gas was 

 collected, and found to contain nitrogen correspond- 

 ing to an excretion of over 8 mgr. per hour and 

 kilogram of body-weight. This result was obtained 

 when the animals were located in free air. In a sec- 

 ond series the head of the animal was cemented into 

 the apparatus. The excretion sank to 2-3 mgr. per 

 hour and kilogram. Finally, in a third series, the 

 whole body of the animal was immersed in a warm 

 bath in order to hinder possible diffusion of atmos- 

 pheric nitrogen into its cavities, and the excretion 

 was reduced to 0.3-0.5 mgr. per hour and kilogram, 

 or to about one-twelfth the amount found by Seegen 

 and Norwak. 



It thus appears that the greater the care taken to 



1 Zeitschr. fur biologie, xvi. 367. 



2 Jahresber. tliier. chem., xi. 382. 



