4OO PRINCIPLES OF AGRICULTURAL CHEMISTRY 



is assumed that the excrement corresponds to the food fed on 

 corresponding days. This assumption is justified if the period 

 of collection is long enough to compensate for the irregularities 

 in elimination of the excrement. A period of only three or four 

 days is likely to give incorrect results. The collection period 

 should not be shorter than six days for pigs, eight days for sheep, 

 and ten days for cattle. 1 



In digestion experiments with dry feeding-stuffs, a sufficient 

 quantity of the feeding-stuffs should be secured before the ex- 

 periment is begun. After ascertaining, by trial, how much the 

 animal will eat, the feeding stuff should be mixed thoroughly, 

 and the quantities to be fed each day should be weighed out care- 

 fully before beginning the experiment ; at the same time, samples 

 should be taken for analysis. 



The animal is fed exactly the same ration for a period of from 

 16 to 1 8 days. The first 6 to 8 days feeding is for the purpose 

 of eliminating residues from the previous ration, and is called the 

 preliminary, or preparatory period. At the end of this period 

 the digestion period begins, in which the excrement is collected 

 for analysis. This lasts about 10 days. The excrement may be 

 secured in rubber bags attached to the animal, or by special stall 

 arrangements which prevent the solid excrement from being 

 scattered or mixed with urine or bedding. With small animals, 

 the excrement is collected every 24 hours, mixed thoroughly, and 

 an aliquot part dried at a low temperature (60-70 C.). With 

 horses and cattle, the aliquot should be taken every 12 hours, as 

 the large masses remain warm and ferment rapidly. After dry- 

 ing, the samples are mixed and analyzed. If green feeds, silage, 

 or similar materials are to be tested, equal quantities should be 

 weighed for feeding each day, and a sample for analysis should 

 also be taken every day and dried at once. The quantity of 

 feed should be adjusted to the appetite of the animal before the 

 preliminary feeding period begins. Residues, even when weighed 

 and analyzed, introduce disturbances and diminish the value of 

 the work. 



1 See Kellner, Exp. Sta. Record 9, p. 504. 



