334 RESPIRATION. 



there is an excretion of nitrogen, although only in extremely small 

 quantity. According to the former of these inquirers, the expired 

 air was about 0*402 (by volume) richer in nitrogen than the 

 inspired air ; whilst the latter observers found in their experiments 

 on animals, that for every 10,000 parts by weight of absorbed 

 oxygen, from 8 to 133 parts of nitrogen were developed in the 

 lungs. Boussingault* had already endeavoured at an earlier period 

 to prove this fact by an indirect method, namely, by comparing 

 the quantity of nitrogen taken into the system with the food, with 

 that contained in the fluid and solid excrements, and the result 

 was, that the quantity of nitrogen present in the excrements was 

 below the amount taken up with the food, and hence it was con- 

 cluded that the deficient quantity of nitrogen must have been 

 excreted from the organism through the lungs. Boussingault 

 found that the relative weights of the exhaled nitrogen and the 

 expired carbonic acid were nearly as 1 : 100. Barralf obtained 

 the same result in his experiments on men, for according to him 

 the quantity of exhaled nitrogen amounts to about l-100th of the 

 quantity of the excreted carbonic acid. We have already observed 

 (in vol. i, p. 453) that a portion of the nitrogen occurs in the 

 expired air under the form of ammonia. 



In addition to these very slight traces of ammonia, the expired 

 air not unfrequently also contains volatile substances which have 

 been taken with the food, such as alcohol, phosphorus, camphor, 

 and ethereal oils ; and even when no such substances can be 

 detected in the food, small quantities of an organic carbo- 

 hydrogen are found in the expired air. The reddening which 

 sulphuric acid undergoes when used for the purpose of drying the 

 expired air also indicates this fact ; but when, as in most experi- 

 ments on animals, certain products of perspiration are intermixed 

 with the expired air, this coloration may depend upon the gases 

 of the intestinal exhalations, or in case the second of the methods 

 above indicated have been employed, it may be owing to the 

 presence of mechanically adhering organic parts, as, for instance, 

 dust from the skin of the animal. But even where respired air, 

 in which no impurities are present has been employed, a slight 

 colouring of the acid may be constantly observed after the air has 

 been suffered to pass uninterruptedly through a sulphuric acid 

 apparatus. It seems tolerably well established, from the very exact 



* Ann. de Chim. et de Phys. 2 Ser. T. 61, p. 128 ; and 3 S^r. T. 11, p. 433, 

 andT. 12, p. 153. 



t Compt.rend. T. 27, p. 361, 



