412 NUTRITION. 



direct bearing upon the phenomena of nutrition, which we are 

 about to consider, its elucidation being to a certain extent the 

 first point from which we are able to obtain an insight into the 

 quantitative relations of the metamorphosis of matter during nutri- 

 tion. Unfortunately, however, we possess only very imperfect 

 investigations on this subject, the most complete of which are 

 those which were made by Boussingault* on ducks. These animals 

 were left without food forSGhours before the beginning of each expe- 

 riment, although they were allowed to take water during this time; 

 for th e purpose of the actual experiment the food in question was 

 introduced in the form of balls ; the ducks were killed at different 

 intervals of time, and the excrements, as well as the contents of 

 the intestines were analysed with special reference to the quantity 

 of fat and nutrient matters still remaining unresorbed. It was of 

 course necessary to determine before each series of experiments 

 the quantity of fat and of other matters, which generally remained 

 i n the intestine even after 36 hours 5 fasting. However carefully 

 these investigations may be conducted, we ought to exercise 

 considerable caution in deducing any conclusions from the results 

 thus obtained. For independently of the fact, that these results 

 obtained from ducks do not admit of comparison with the corre- 

 sponding relations of higher animals, the birds thus experimented 

 upon not only obtained the articles of food given to them, 

 unmixed with other substances, but also in a form to which they 

 were entirely unaccustomed. We have already seen under the 

 head of " Digestion ," L that individual articles of food, as for instance, 

 the nitrogenous matters, when they are introduced into the intes- 

 tinal canal independently of other substances, are less easily 

 digested ; there would, therefore, be less matter to be resorbed in 

 these cases than usually occurs under the ordinary relations of 

 nutrition in ducks. Nor can any one deny, that food differing so 

 much from the ordinary kind, as rolled up pieces of dry cheese or 

 gelatin, must be quite inadequate to afford any conclusive evidence 

 of the normal relations of nutrition in ducks. If, however, all these 

 objections were obviated, and the contents of the intestine and the 

 excrements were not only weighed, but also analysed, the circum- 

 stance that the intestinal excretion was different during digestion 

 from what it was in a state of fasting, must essentially influence 

 the accuracy of the results; for we know, and shall have still further 

 occasion to see in the course of our considerations, that something 

 more than the undigested and indigestible remains of the nutrient 

 * Ann. de Chim. et dc Phys. 3 Ser., T. 18, p. 444-478. 



