810 EXPERIMENT STATION RECORD. 



Proper means must be taken for preventing fermentation of the 

 excretory products when they are retained for analysis. To this end 

 the feces should be removed as soon as possible from the bag in which 

 they are collected, and should be weighed, sampled, and dried at once. 

 In winter the cold weather prevents the fermentation of the urine. In 

 summer a known quantity of preservative material — for instance, sul- 

 phuric acid, formic aldehyde, or thymol — may be added to the urine. 

 The apparatus for collecting the urine must be rinsed at least once in 

 48 hours with a disinfecting solution (10 per cent formic aldehyde), and 

 afterwards with pure water. When only the nitrogen in the urine is 

 determined it is a matter of indifference which preservative is used. If 

 the carbon is also determined then the use of sulphuric acid or cold 

 storage must be resorted to, since both formic aldehyde and thymol 

 contain carbon. If the mineral matter is also to be determined then 

 sulphuric acid cau not be used and a low temperature is the only 

 method available. 



Care must be taken that all the food is eaten or that the uneaten 

 residue is weighed. The same precaution applies to water also. 



During the preliminary period the weight of the animal should be 

 accurately determined daily. During the experiment proper this fac- 

 tor may also be determined if the urine and feces are collected as soon 

 as they are excreted. However, it is not a matter of great importance 

 to determine the weight during this period unless it is long. When the 

 weight remains constant for 2 or 3 months, or when it slowly increases 

 or diminishes during such a period, this factor is of importance in draw- 

 ing deductions. Otherwise the variations iu water content of the intes- 

 tinal tract, and hence the excretion of a larger or smaller quantity of 

 feces on a given day, render this determination unreliable. Aside from 

 such irregularities an animal may lose fat and flesh daily — that is, be 

 in a condition of partial starvation — while the body weight remains 

 constant or even increases. This is the case when the fatty tissue and 

 protein (cells and cell contents) are broken down and replaced by 

 water. In other words, if the experimental period is short a loss of 

 body material may be covered by the large gain of water. The con- 

 verse is also true. An animal poor in flesh but with a high water 

 content may gain flesh and fat and at the same time lose weight owing 

 to a diminution of the water in the tissues. 



ANALYSIS OF THE MATERIALS. 



In the analysis of the total food, the uneaten residue, and the feces 

 it is important to determine the amount of sand and pure ash (includ- 

 ing silica) in addition to the total ash. The sand mixed with the food 

 passes through the animal undigested, and if the amount consumed is 

 recovered it is an indication that the analytical work is to be depended 

 upon. 



Organic material in food and excretory products is made up of nitro- 

 genous and nitrogen-free substances. The former include protein, 



