FEEDING OF ANIMALS. 333 



100-lb. sample, of 8.03, and to the other or duplicate one, of 

 10.55 per cent. 



Such, then, were the results of the earlier experiments Review of 

 made by various investigators, to determine whether or not res * ats <*? 

 there was any loss of nitrogen in the feeding of animals nitrogen. 

 beyond that stored up in their increase. It will be observed 

 that, with the exception of the turtle-doves experimented 

 upon by Boussingault, all the other results were obtained 

 with the animals of the farm ; and in all cases, excepting 

 those of the experiments at Eothamsted with pigs and with 

 sheep, and at Woburn with oxen, the animals were assumed 

 to be fed on only sustenance rations, and no allowance was 

 made in the calculations for any increase or loss in their 

 weight. It has been seen that in every case, excepting in the 

 experiment with Henneberg's Ox No. 2, and in the experi- 

 ments at Eothamsted with pigs in 1862, the figures indicate 

 a notable, and in some a very considerable, loss of nitrogen ; 

 which, assuming it to be not explained by storing up of 

 nitrogen in the animal, or deficient evacuation, might be 

 supposed to point to a probable loss by respiration, or perspira- 

 tion, or both. 



From a study in much detail of the direct experiments on 

 respiration and perspiration which have been referred to, we 

 ourselves have been disposed to conclude that there was no 

 material exhalation of either free nitrogen or of its com- 

 pounds. Further, notwithstanding our own early results 

 with pigs, those with sheep, and those at Woburn with oxen, 

 all indicated more or less, and sometimes a considerable loss, 

 the observations made during the conduct of the investi- Loss of 

 gations so fully impressed us with the liability to error, ^l^Z] 

 especially on the side of loss, that we have always considered 

 it doubtful whether there was in reality any material loss at 

 all. In the first place, there is the uncertainty in the estima- 

 tion of the changes in the weight of the body — whether to 

 attribute them to increase or loss of its fixed substance, or to 

 excess or deficiency in the evacuations in relation to the food 

 consumed within the period of experiment; and there are, 

 besides, great difficulties to be overcome, both in the com- 

 plete collection, the proper sampling, and the preparation, 

 without change, of the excreted matters ; and there are also 

 special difficulties in the adaptation of analytical methods to 

 secure exact representative results. Indeed, most of the 

 results so far quoted, whether of ourselves or others, must be 

 looked upon as little more than pioneer ; though, taken as 

 such, the experience gained has proved to be of essential 

 value in directing attention to the difficulties and sources 

 of error incident to such work, and to the improve- 



