THE BALANCE OF NUTRITION 203 



a demonstration that nitrogen leaves the body only in the 

 combined form in the visible excreta. 



289. Determination of nitrogen balance. There being no 

 excretion of gaseous nitrogen, a determination of the nitrogen 

 balance requires simply a determination of the amounts of this 

 element contained in the feed and in the visible excreta. Evi- 

 dently this end is already partially attained in a digestion ex- 

 periment (158). It is only necessary in addition to provide 

 for the quantitative collection and analysis of the urine and, in 

 very accurate experiments, of the perspiration and of the epi- 

 dermal excreta, in order to obtain data for a comparison of the 

 income and outgo of nitrogen, and the same precautions as to 

 length of period, uniformity of feeding, etc., which are necessary 

 in a digestion experiment, suffice also to render the results of a 

 balance experiment representative. 



290. Example of a nitrogen balance experiment. The digestion 

 experiment with clover hay used as an example in Chapter III (160) 

 may serve also to illustrate the nature of a nitrogen balance experi- 

 ment. In that experiment the hay consumed daily contained 3.144 

 Kgs. of dry matter and the daily feces 1.267 Kgs., while the average 

 daily weight of the urine for g days was 5.449 Kgs. Analysis showed 

 the following percentages of nitrogen : 



In dry matter of hay 2.271 % 



In dry matter of feces 2.240% 



In fresh urine 1.074% 



The brushings of the steer (hair, dandruff, etc.) were found to con- 

 tain 1.87 grams of nitrogen per day. The daily nitrogen balance 

 may accordingly be computed as follows, showing a loss from the body 

 which, of course, must be placed in the income column to complete the 

 balance. 



TABLE 22. EXAMPLE OF A NITROGEN BALANCE 



