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��TCfsy nniong physiologists; one ^rhool m.iintaining, and SDother deny log, that It is In be interpreted as shdwing an excretion of gaseous Tiltrogeii.
There Is one fact which reniiers the resiiirs ob- Uined by the experimental meihnil just menlioned inconclnsire either for or against an excretion of free nitmgen; it is that the animal eiiperimented upon ii)«y either ^Hin or lose nitrofrenous matter from the tissues of its body during the experiment™ If the former take place, the excretion of nitrojien is diminished bj that amount: it the latter happen, It is intrrcosed. But, while iuch gain or loss of nitro- genous matter l>y the body may undoubtedly take [ilitce, we have no means of proving that a. Email gain or loss haa or has not occurred in any given experiment. If In snrae trial Ihs nitrogen of the excreta exactly equal that of the food, the advocate of the excretion of gaseous nitrogen can say that a certain (nnknown) amount of nitrogen mai/ have been lost from the body of the animal, and. by chance, the same amount mny have been excreted as If an experiment show a deficiency of nitrogen I the excreta, the denier of the excretion of free Bltn^en can say that exactly that amount of nitrogen r have lieeo gained by the animal. Plainly, Clther of these possibilities can be either proved or bproved by this method of experiment. A n^sori to an investigation of the respiratory tducts naturally suggest:} itself. The experiment, lOngh a difficult one, has been made; but the re- ttta have not, as might have been hoped, sufficed to "iclde the question deSnitnly.
f It should be remembered that the amount of n eicreled as gas must, in any case, be small. e large deficit found by the earlier experimenters Kdniversally acknowledged to have been erroneous. ling this In mind, it is evident, that, as already Int^ out, a single experiment by the first metliod la coraparallvely little weight. But very many such erimonts have been made, and, when properly ature animals, with food just sufO- t to maintain them without gain or loss of weight), they all i^ee lu 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 obMrvers, whose results chance to lie before me, nineteen show an excess ot nitrogen in the excreta, and twenty-tour 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 deflciency from 0.02 % to fl.7 %. Many more observations might be 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 ot gaseoiia nitrogen, particularly Seegcn and Korwak In Vienna, have attacked these results upon the side of the ana- IjUcal methods employed, claiming that the process la-lime process) used for estimating nitrogen Ires too low results. It has been shown, however.
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��by several chemt?Is, Ibat lliis is not the case when the process is properly performed; while some recent trials by Gruber' show, that, when the so-called 'absolute method ' [or nitrogen Is employed, substan- tially the same results are reacheil.
The main reliance ot 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 absoriied bj caustic potash. At the close of the experiment the air iu 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 Kegnaull and Reiaet 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 ot nitrogen was observed, e.^pecially during hunger. In experiments with larger animals (sheep and calves), in ti larger apparatus, the apparent excretion was quite considei^ able.
Seegen and Jlorwak in Vienna have reported nu- merous trials with a. simplified form of Regnault and Keiset's apparatus, all ot 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 reaulls of the other.
Some recent experiments by Leo^ are of much In- terest in this connection. He worked with rabbits, which were tracheotomiied 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. Iu 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-O..5 mgr. per hour and kilogram, or to about one-twelfth the amount found by Seegen and Norwak.
It thiw appears that the greater the care taken to
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