FEEDING OF ANIMALS. 325 



stituents, and of comparatively little by the action of its pro- 

 ducts of decomposition within the soil Indeed, the most What pro- 

 important point to consider is — what proportion of the nitro- v ^o°qen 

 gen of the food remains for manure ? As has been shown, in food re- 

 sold as will be further illustrated presently, only a compara- wl « lw */ or 

 tively small proportion is carried on in animal increase ; but 

 a much larger amount is lost to the manure in the production 

 of milk. But the further questions arise — Is there any, so 

 to speak, vital exhalation of nitrogen, or of any compounds 

 of it, by the animal ? Or, may we estimate that the whole 

 of that consumed which is not carried off in the animal in- 

 crease, or in milk, will be found in the solid and liquid de- 

 jections, and so remain for manure ? Or, on the other hand, 

 is there any assimilation by the animal, of the free nitrogen 

 of the atmosphere ? The further practical question still 

 remains — Is there any material loss of nitrogen after the 

 solid and liquid excretions leave the body, and before their 

 utilisation within the soil for the production of future crops ? 



First, then, is there any vital exhalation by the animal of Exhala- 

 nitrogen or of any of its compounds ? _ aZrptfon 



Obviously, this is a question which could not be ex peri- of nitrogen 

 mentally investigated before definite knowledge was attained b y animals - 

 in regard to the composition of the atmosphere. But after 

 such knowledge had been acquired, rather more than a 

 century ago, the subject of the mutual relations of the at- 

 mosphere, and of vegetable and animal growth, came to be 

 studied ; and, among other points, it was sought to determine 

 whether, on the one hand, the free nitrogen was assimilated 

 by animals ? or, on the other, whether it was exhaled, at the 

 expense of the nitrogenous substance of the food, of the 

 blood, or of the more fixed substance of the body ? 



Commencing towards the end of the last century, numer- Various 

 ous investigations have been undertaken from various points ™™^ 9a ~ 

 of view bearing upon the subject; and among the investi- 

 gators or writers may be named — Lavoisier, Laplace, Seguin, 

 Dalton, Sir H. Davy, Pfaff, Provencal and Humboldt, Allen 

 and Pepys, Despretz and Dulong, Brunner and Valentin, 

 Marchand, von Erlach, Baumert, Kegnault and Eeiset, Ber- 

 thollet, Milne-Edwards, and C. G. Lehmann ; besides others 

 more recently. 



It is impossible shortly, and at the same time adequately, 

 either to describe or to criticise the numerous and, upon the 

 whole, discordant results, that have been obtained in regard 

 to the question of the assimilation or exhalation of free nitro- 

 gen by animals. It is noticeable that the earlier investi- 

 gators, Lavoisier, Laplace, and Seguin, concluded that the 

 amount of nitrogen expired was neither more nor less than 



