Loss in Respiration and Digestion 307 



is gradually changed into humus by the activities of 

 the latter. In this change, a portion of the inert plant- 

 food in the manure, as well as of that in the soil, is ren- 

 dered available to the crops. 



Animal manures, green-manures, and other organic 

 fertilizers possess, therefore, a value over and above that 

 possessed by purely mineral carriers of plant-food. In 

 measuring the utility of organic materials, allowances 

 should be made for the quantity of bacterial food con- 

 tained in them. 



Losses of elements in the animal. — In animal manures 

 the organic matter is derived from the food and the litter. 

 However, much of it never reappears in the manure. 

 A large part of it is burned up in the body in order to 

 provide the animal with the necessary energy. It is 

 also exhaled from the lungs as carbon dioxid and water. 

 It was found by Henneberg that a steer thus exhaled 

 in one day fifty pounds of carbon dioxid and water. 

 Another portion of the organic matter in the food is 

 changed into gaseous products by bacteria in the in- 

 testinal tract, respiration calorimeter experiments show- 

 ing the presence of considerable quantities of marsh- 

 gas in the gaseous excreta of herbivorous animals. The 

 total amount of organic matter burned up in the animal 

 body may thus amount to more than half of that in 

 the food consumed. 



In passing through the animal body, the food suffers 

 a loss, not of carbon and hydrogen alone, but, also, of 

 nitrogen, phosphoric acid and potash. In fattening 

 steers, as much as 5 to 10 per cent of the food nitrogen 

 may be retained, while in milch cows the amount se- 



