66 



METABOLISM EXPERIMENTS AND THE DEDUCTIONS DRAWN 



FROM THEM. 



There are man}- other complicated questions in horse feeding which 

 have received much attention from investigators. As in experiments 

 with man, the factors which serve as indices of changes going on in 

 the body have been studied in this connection, the principal ones 

 being (1) the balance of income and outgo of nitrogen, or nitrogen and 

 carbon (as in metabolism experiments and respiration experiments), 

 which is quickly modilied by variations in food, work, and other con- 

 ditions; (2) the amount of carbon dioxid produced per second as 

 compared with the amount of oxygen consumed from the air, i. e., 

 the respiratory quotient, which changes very quickly when any change 

 takes place in the vital processes or in other forms of internal muscular 

 work or when the amount of external muscular work varies. In deter- 

 mining the income and outgo of nitrogen the food, urine, and feces 

 must be measured, and the amount of nitrogen in each determined. 

 No very complicated apparatus is required, and such experiments are 

 comparatively numerous. Where the income and outgo of carbon is 

 determined, as well as that of nitrogen, the experiments necessitate the 

 use of a respiration apparatus. In such experiments it is possible to 

 calculate the balance of income and outgo of matter. If at the same 

 time devices are used which permit the measurement of heat, the bal- 

 ance of income and outgo of energy may be studied also. The experi- 

 ments of Boussingault, Wolff, Kellner, Hofmeister, Henneberg, and 

 others, in which the balance of income and outgo of nitrogen were 

 determined, have led to a number of interesting conclusions, some of 

 which have already been referred to. Others follow. 



Boussingault, who was one of the first to study these problems, 

 showed that no nitrogen was assimilated from the air, but that all 

 which was used in the body came -from nitrogen compounds con- 

 sumed in the food— a very important deduction, since it showed 

 that no nitrogen could be taken from the air, and, that nitrogenous food 

 was essential. The investigations of Grandeau, Leclerc, and their 

 associates form one of the most extended studies ever undertaken 

 with farm animals. The work was carried on with a very large num- 

 ber of horses belonging to one of the Paris cab companies, and extended 

 over many years. There were seven series of experiments.'' In the 

 first, a mixed ration consisting of " maize cake," horse beans, maize, 

 oats, hay, and straw was fed. The maize cake was made from starch 

 factory and distillery waste, and contained a considerable portion of 

 potato and barley as well as corn refuse. In the second series the 



a Ann. Sci. Agron., 1884, II, p. 325; 1885, I, p. 326; 1886, II, p. 351; 1888, II, p. 211; 

 1892, I, p. 1; 1893, I, p. 1; 1896, II, p. 113. 



