GENERAL CONSIDERATIONS 241 



act, the starch equivalent of the rations under 

 comparison must be kept the same, as must all 

 other conditions, except on the one point which is 

 being tested. Further, a chemical and micro- 

 scopical examination is also essential, for it is 

 only by these means that the nutritive value of 

 the food-stuff can be judged. In very many cases, 

 whether the investigations are concerned with 

 fattening, working, or breeding stock, the live weight 

 is the most important, and often the only means of 

 judging of the action of the food. Owing to the 

 considerable differences in weight, due to irregular 

 excretion of dung and urine and to the unequal 

 consumption of drinking water, it is not enough to 

 weigh the animals every fourteen days or so, but 

 the weighing must always be done on three con- 

 secutive days at exactly the same time, and pre- 

 ferably before the first meal. The length of the 

 experiment ought also not to be too short with 

 fattening and working animals ; the minimum 

 should be two months, and it is even better to 

 take a longer period, particularly in feeding groups 

 of animals, which ought to be carried on until 

 ready for the butcher. Important manifestations, 

 such as loss of appetite, cessation of growth in 

 young animals, diminished staying power in working 

 animals, often only appear after the investigation 

 has been in progress for a length of time. 



All other conditions, such as temperature of the 



