1044 EXPERIMENT STATION RECORD. 



of water throuf^h tho u))sorber.s, the rate at which heat is i-cmovod 

 thi()ii<;h tlic water current may be so rej^ulated as to keep the leiiipera- 

 tiire of the iiitei-ior constant within very small limits, wiiile the slight 

 varhitions are made to balance each other in the course of an expeii- 

 ment, so that there is practieall}' no capacity correction. Under these 

 conditions, all the heat evolved by tlie animal nnist leave the apparatus 

 either as sensible heat in the wat(>r current or as the latent heat of 

 water vapor. 



In practice, of course, corrections have to be made for any heat 

 introduced or removed as sensi))le heat in t\w feed, excreta, etc. The 

 friction of the water in the coil of copper pipes is also the source of a 

 minute amount of heat, which is computed from the volume of water 

 and th(^ fall in i)rcssure in passing- through the pipes. This difference 

 in pressure also afiects slig'htl}' the readings of the thermometers, 

 tending to make those in the ingoing water relatively higher than 

 those in the outcoming water. The small correction for this differ- 

 ence has been determined experimentally within the range of pres- 

 sures used. 



BUILDING. 



The l)uilding in which the apparatus is housed is of brick, with 

 heavy walls containing an air space to aid in maintaining uniform tem- 

 perature. The floor is of concrete, the ceiling high enough to leave 

 about 3i feet clear space al)ove the top of the respiration chamber, 

 which stands upon three l)rick piers a))out 18 inches above the floor 

 of the room. In this wa}' any difficult}^ arising from differences in 

 temperature at different points in the room has been avoided. 



EXPERIMENTS. 



The experiments thus far made have been of 48 hours' duration, 

 this period being subdivided into subperiods of 12 hours each. The 

 animal is placed in the apparatus 5 or 6 hours ))eforethe beginning of 

 the experunent, which has been conveniently placed at 6 p. m. By 

 this time the apparatus has come into equilil)rium, and it is only nec- 

 essary to shift the current of air from one set of cans and absorption 

 apparatus to another in order to begin the experiment. 



The experiments have followed each other at an average interval of 

 from two to three weeks. During the intervening time the animal 

 stands in an adjoining room in a stall which is provided w ith appliances 

 for the quantitative collection of the visible excreta. An actual exper- 

 iment requires the services of at least seven men, exclusive of the 

 assistant in charge of the feeding and collection of excreta. Three 

 series of experiments have thus far been made, the results of the first 

 of which have l>een recentl}^ reviewed in these pages (E. S. R., 15, 

 p. 799). 



