7;i8 EXPERIMENT STATION RECORD. 



Tlioso tirnit>-s iimkc the appiU'iitus specially adapted to studies of 

 sueh (piestions as the cneroy rcciuired to dioest and assimilate different 

 classes of feedinir stuffs. It is o])vious that more energy will be used 

 up in asslmilatiiiii' the nutritive material from a feed like timothy hay, 

 containing relatively large amounts of crude til)cr and woody sub- 

 stances, than from a concentrated feed like corn meal, and that this 

 factor Avill affect the net value of the feed for the nutrition of the 

 animal. Such dillerences are not taken account of in ordinarj^ studies 

 of the composition and digestibility of feeds. Hitherto they have 

 been studied very largely by Zuntz's method of observing the varia- 

 tions in the respirator}^ (piotient; that is, the ratio of oxygen con- 

 sumed to the carbon dioxid excreted. Dr. Armsby's apparatus fur- 

 nishes another way of approaching such problems and one in which 

 it is possible to control the experimental conditions and judge of the 

 changes going on in the body more accurately. 



That the first series of experiments with this apparatus should have 

 given results of so nnich interest, both in their scientific aspects and 

 froju a practical standpoint, is especially gratifying. The conclusion 

 reached that a maintenance ration is not a constant quantity, but a varia- 

 ble one depending upon the kind of food used, is of fundamental impor- 

 tance, as are also the closely related deductions which have to do with 

 the replacing value of nutrients. There is indication that Rubner's 

 law regarding the replacing value of nutrients, which has l)een held 

 for so many yesLi's, is subject to certain limitations and will need modi- 

 fication in the light of the energy requirements for digestion and 

 assimilation. Indeed, Rubner's original conception in regard to this 

 matter has been considerably^ modified in his recent book. 



The apparatus affords an opportunity for following up a great variety 

 of important lines of investigation and for checking the results secured 

 by the more practical methods of feeding experiments. The difference 

 found in the above experiment between the energy used up by the 

 animal when standing and wdien lying down suggests the importance 

 of reducing muscular activity to a minimum during the fattening 

 period. Furthermore, the fact that on a maintenance ration and when 

 closely confined the steer produced more heat than was required to 

 maintain the bodj^ temperature has a bearing on the contested point 

 as to whether steers should be fattened out of doors or in stables in 

 cold weather. It seems evident from Dr. Armsby's data that steers 

 on heavy or fattening rations are really developing an excess of heat, 

 and hence would not need to draw upon their food for any increased 

 supply when fed out of doors. This supports and explains Waters's 

 conclusions of several years ago. Some of the observations already 

 made also have a decided bearing on the problem of stable hygiene 

 and ventilation; and, in a word, it is true of this as of the Atwater- 

 Rosa apparatus that the possible lines of investigation range from the 

 most practical to the most technical subjects. 



