100 MAINE STATE COLLEGE 



illustrated in the experiments now under consideration. The pigs 

 of Lot 1 grained 199 lbs. in the same time that the pigs of Lot 2 

 gained 188 lbs., the amount of digestible food being nearly the 

 same, and the nutritive ratios being 1:3.6 and 1 : 6.0 respectively. 

 In an eighty-eight day period with the animals of Lots 3 and 4 a 

 nutritive ratio of 1:5.6 with Lot 3 did practically the same work 

 as a ratio of 1 : 44 with Lot 4, the increase in weight being 174 and 

 181 lbs. in the two cases. It seems that in these feeding ti'ials 

 with swine, the various rations having a nutritive ratio of 1 : 6.1, 

 or below, were equally efficient, and much more efficient than 

 rations with a ratio of 1 : 9.0 or thereabouts. It is fair to conclude 

 from this that in feeding for any particular purpose the proportion 

 of protein must be kept up to a certain standard if the maximum 

 results are to be attained, as a departure from this standard in the 

 direction of less protein results in a diminished production. On 

 the other hand, a deviation from this standard by increasing the 

 proportion of protein seems to be without marked affect, within 

 certain limits, at least. How shall we explain this? Let us 

 suppose the ration is intended for a growing animal. A certain 

 part of the new substance which constitutes growth consists of 

 muscular tissue and other nitrogenous compounds, the only source 

 of which is the protein of the food. Protein also plays a necessary, 

 though unexplained, part in muscular activity. If, therefore, the 

 the food is deficient in protein, growth must either be checked or 

 become abnormal, and it is the former that is most likely to occur. 

 But whenever a ration contains protein in excess of the necessary 

 amount, the results are quite different. Although protein is the 

 sole source of certain compounds essential to growth, it may and 

 does perform other offices, such as the production of heat. When, 

 therefore, the protein of the food is increased and the carbohyd- 

 rates decreased, the former may furnish the fat or heat otherwise 

 derived from the latter. To be sure the one class of compounds 

 does not replace the other pound for pound. According to the 

 estimates of physiological chemists a hundred parts of protein may 

 furnish 51 parts, while the maximum product of one hundred parts 

 of starch would be only 41 parts, of fat. The heat producing 

 power of protein and of starch is not greatly different. These 

 differences are not such, however, as to be easily detected by the 

 crude methods of a practical experiment, and so there has some- 

 times been but little apparent effect from quite a wide variation of 

 the nutritive ratio in past feeding trials. 



