326 



THE EOTHAMSTED EXPERIMENTS. 



Investiga- 

 tions not 

 conclusive. 



Loss of 

 nitrogen 

 in breath- 

 ing and 

 sioeating. 



that inspired ; and in this view they are in the main sup- 

 ported by the conclusions, though not entirely by the results, 

 of Allen and Pepys, of Brunner and Valentin, and von 

 Erlach. In favour of the view that free nitrogen is ab- 

 sorbed and assimilated, may be cited the opinions of Sir 

 Humphrey Davy and. of Pfaff, so far as certain warm-blooded 

 animals are concerned ; and of Provencal and Humboldt, 

 and of Baumert, in regard to fish. On the other hand, that 

 there is evolution of free nitrogen has been concluded, by 

 Sir H. Davy, Berthollet, Dulong and Despretz, Magnus, 

 Marchand, Grassi, Eegnault and Eeiset, and C. G. Lehmann. 



In regard to evolution, the most extensive and elaborate 

 experiments are those of Eegnault and Eeiset. But the 

 amounts which their results indicated would imply the loss, 

 in that way, of an incredibly large proportion of the total 

 nitrogen consumed in the food ; whilst Liebig estimated that 

 the evolution which Dulong assumed was so great that, in 

 the case of one of the experimental animals, the whole of the 

 nitrogen of the body would be lost in seven days ; and that, 

 at the rate assumed by Despretz, the nitrogen of one pound 

 of flesh would go off in thirty-one hours. 



Then, the results indicating absorption are the most pro- 

 nounced in the experiments with fish. The question arises, 

 therefore, whether in their case the result may not be ex- 

 plained by supposing that oxygen has been absorbed from 

 the air within the body, especially in the swimming bladder, 

 and nitrogen stored up in its place, under the conditions of 

 limited supply of oxygen from external sources to which 

 the animals have generally been subjected during experiment. 



Upon the whole it must be concluded that, from a variety 

 of causes, connected sometimes with the conditions under 

 which the animals were placed under experiment, sometimes 

 with the circumstances under which the samples assumed to 

 represent the inspired and expired air, respectively, were taken 

 for analysis, and sometimes with the methods of analysis 

 themselves, the results of the experiments on respiration 

 which have been referred to, have not been sufficiently free 

 from doubt to be accepted as establishing so important a con- 

 clusion as either the assimilation of free nitrogen by animals, 

 or the evolution of it from its compounds within the body. 



The next point to consider is — whether there is any loss of 

 ammonia, or of other compounds of nitrogen, in the breath, or 

 by the skin. 



Louis Thompson, Thiry, Grouven, and others, have found 

 some emanation of ammonia ; but Lossen, and others, consider 

 it doubtful whether the ammonia in the air itself might not 

 account for the results. 



