46 SCIENTIFIC FEEDING OF ANIMALS 



quantities of nitrogen-containing substances vola- 

 tilise, so it is generally preferable to analyse the 

 fresh dung. The previous feeding of the animal 

 exercises considerable influence on the excretion 

 of urine, so care must be taken that the nitrogen 

 in the urine is constant before the real experiment 

 begins. 



2. A determination of the increase of fat in an 

 animal body is only possible when, in addition to 

 the nitrogen, all the carbon that goes into and 

 leaves the body is known. As the animal gives 

 out large quantities of carbon-containing sub- 

 stances (carbon dioxide and marsh gas principally) 

 from the lungs, skin and rectum, it is essential to 

 determine these gaseous products in addition to 

 the solids. The analysis of the gases usually 

 takes place in the Pettenkofer respiration chamber 

 which will be described later. An example will 

 show what can be learnt from such investigations. 

 An ox was given the following amounts of nitrogen 

 and carbon in the food and water daily : 186-47 

 gr. nitrogen and 5564-5 gr. carbon ; excreted in 

 urine, dung, and breath 179-24 gr. nitrogen and 

 4892-0 gr. carbon ; remaining in body 7-23 gr. 

 nitrogen and 672-5 gr. carbon. 



Pure dry flesh contains 16-67% nitrogen and 

 52-54% carbon, so the addition of 7-23 gr. nitrogen 

 equals 43-4 gr. of dry flesh containing 22-8 gr. of 

 carbon. For the increase of fat there remain, 



