ADAPTATION OF EXCREMENT FOR MANURE. 275 



even when it destroys the green blades it brings on new 

 shoots with fresh luxuriance.* 



It belongs to physiology to explain why vegetable matter is 

 more sensibly active as a manure after it has passed through 

 the body of an animal, than if applied to the land in an un- 

 masticated and undigested state. Of this no more concise 

 explanation can be afforded than that given in the following 

 quotation from the late Professor Johnston's work : " Every- 

 thing which enters the body in the form of food must escape 

 from the body in one or other of three different channels. It 

 must be breathed out from the lungs, perspired by the skin, or 

 rejected in the solid or liquid excretions. We have already 

 seen that the function of the lungs is to give off carbon in the 

 form of carbonic acid, while they drink in oxygen from the air ; 

 and that the quantity of carbon thus given off by a healthy 

 man varies from five to thirteen or more ounces in the twenty- 

 four hours. From the skin also carbon escapes along with a 

 small and variable proportion of saline matter. The weight of 

 carbon given off by the skin has not been accurately ascertained. 

 Let us leave it out of view for a moment, and consider solely 

 the effect of respiration upon the nature of the solid and liquid 

 excretions. 



" Suppose a healthy man, taking a moderate degree of exer- 

 cise, to give off from his lungs six ounces of carbon in twenty- 

 four hours, and to eat during the same time two pounds of 

 potatoes, half a pound of beef, and half a pound of bread, then 

 he has taken in his food 



Carbon. Nitrogen. Saline matter. 



Grains. Grains. Grains. 



In the potatoes, . 1716 47 196 



In the bread, . . 1004 34 22 



In the beef, . 790 120 35 



3510 201 253 



* Johnston, ' Agricultural Chemistry, ' p. 



