192 The Feeding of Animals 



utilitarian to be of little value, we now see how di- 

 rectly they are contributing to human progress and 

 welfare. 



To the above information has been added through 

 physiological investigations a knowledge of the ways 

 in which the several food compounds are transformed 

 in digestion and in other metabolic changes, the 

 avenues along which these compounds travel, and the 

 ways in which their products of decomposition are dis- 

 charged from the animal organism. We have learned 

 how to distinguish between the digested and undi- 

 gested food, have demonstrated that all the nitrogen 

 of the decomposed proteids passes oif in the urine, 

 have measured the combustion of the nutrients and 

 have learned how to strike a balance between the in- 

 come and outgo of the animal body. It is now possi- 

 ble to determine with reasonable accuracy just how 

 much substance is retained or lost from the body of 

 the experimental animal while eating a given ration, and 

 what is the nature of the gain or loss. Very recently 

 means have also been devised for measuring the heat 

 given off by a man or an animal in order to ascertain 

 the actual physiological values of different feeding 

 stuffs. 



MORE ACCURATE METHODS OP INVESTIGATION 



In applying the principles and facts of chemistry 

 and physiology, the first advance from the ultra -prac- 

 tical feeding experiment in the direction of an accurate 

 history of wliat occurs when the animal is eating a 



