376 ORIGIN OF ArvI3IAL PRINCIPLES. 



rus, sulphur, and chlorine, calcium, magnesium, srdium, potassium 

 and iron, as they are all encountered in the food ■ j are they all en 

 countered in the body, and also in the excretions cfan animal ; ano 

 it seems certain, that no one of these primary or simple substance* 

 can be wanting in the nutriment without the body very speedih 

 feeling the ill effects of its absence. Iron, for example, is a con 

 stant principle in the coloring matter of the blood ; it also exists ii 

 large quantity in the hair ; and he who should live on food that con 

 tained no trace of it would certainly, and before long, become disor 

 dered in his health. 



In what has just been said, I take it for granted that animals dc 

 not absorb or assimilate any of the azote which forms so large a 

 constituent in the air they breathe ; and I am warranted in this by 

 the researches of every physiologist of any name or distinction. Not 

 only do animals obtain no azote from the atmosphere, but they actu 

 ally exhale it incessantly, as was proved by M. Despretz in the 

 course of his numerous experiments, and as I myself also demon- 

 strated in the inquiries I undertook to ascertain whether herbivorous 

 animals obtained azote from the air or not. The azote exhaled, il 

 was discovered, proceeded entirely from the food consumed by the 

 animal ; a fact which, already of great importance in a physiologi- 

 cal point of view and in reference to general physics, bears at the 

 same time so immediately upon one of the most important questions 

 of agriculture, that I think it well to give the particulars of one of 

 the procedures by which it has been established. 



The experiments in this case were performed on a milch-cow 

 and a full-grown horse, which were placed in stalls so contrived 

 that the droppings and the urine could be collected without loss. 

 Before being made the subjects of experiment, the animals were bal- 

 lasted or fed for a month with the same ration that was furnished to 

 them during the three days and three nights which they passed in 

 the experimental stalls. During the month, the weight of the ani- 

 mals did not vary sensibly, a circumstance wiiich happily enables us 

 to assume that neither did the weight vary during the seventy-two 

 hours when they were under especial observation. 



The cow was foddered with after-math hay and potatoes ; the 

 horse with the same hay and oats. The cjuantities of tbrage were 

 accurately weighed, and their precise degree of moistness and their 

 composition were determined from average samples. The water 

 drunk was measured, its saline and earthy constituents having been 

 previously ascertained. The excrcmentitious matters passed were 

 of course collected with the greatest care ; the excrements, the 

 urine, and the milk were weighed, and the constituti(ui i)f the whole 

 estimated from elementary analyses of average specimens of each 

 The results of the two experini' its are given in this tublc : 



