806 EXPERIMENT STATION RECORD. 



peas 11, cows' milk 8, lupines 7.8, lean meat 4, blood 3.5, protein 3.4. 

 He taught that the food must supply an animal with the specific car- 

 bon value suited to its age. Thus, a sucking calf required a specific 

 carbon value of 8, since the value of milk was 8. The value was 

 greater for older animals. For cattle, horses, and sheep it was between 

 24 and 44, for swine 26, and for milch cows 24. This theory was based 

 entirely on speculation and has never been followed practically. 



Finally an attempt was made to learn how much of the different 

 feeding stuffs was required by trusting the instincts of the animals 

 when given the choice of materials. Thus, a milch cow was given the 

 choice of oil cake, fodder beets, bay, and straw. The amount of each 

 consumed was determined. Such investigations were made by Haub- 

 ner and he soon showed that tlie method was too costly to be of any 

 practical benefit. 



About 1860 Bischoff and Yoit made their classic investigations on 

 nitrogen equilibrium and formulated the laws of growth for Carnivora. 

 Instead of depending on the body weight to show whether a ration 

 was sufficient, the nitrogen excreted in the urine was determined, and 

 further, the excretion of carbon dioxid in the respiratory products was 

 measured by a suitable respiration apparatus. An animal was said to 

 be in equilibrium when the nitrogen and carbon in the excretory prod- 

 ucts equaled the amount consumed in the food, due account being 

 taken of the amounts of carbon and nitrogen lost in epitheliel cells, 

 sweat, mucus, hair, nails, hoofs, and horns. These investigations were 

 at first made with Carnivora only, mainly with dogs and cats, but later 

 were carried on with man. It was much simpler to study the laws 

 of nutrition with Carnivora than Herbivora since their diet is com- 

 paratively simple, the urine is easy to collect and analyze, when fed 

 once a day the feces are excreted daily, and the food does not remain 

 in the intestinal tract longer than 24 hours. Such experiments with 

 Herbivora, and especially with ruminants, are attended with much 

 greater difficulties. Nevertheless Henneberg, Stohmann, Grouven, and 

 others have shown that with ruminants also the general laws of nutri- 

 tion hold good. Such investigations are being carried on at the pres- 

 ent time, and have furnished a large amount of useful information. 

 However, much still remains to be studied. 



E. Wolff has devoted many years to determining the coefficients of 

 digestibility of feeding stuffs by sheep and horses. Kiihn in Mockern 

 and his successor, Kellner, and many others have devoted much time 

 to methods of analysis of feeding stuffs and methods of metabolism 

 experimenting, with a view to establishing a rational basis for animal 

 feeding. A number of the • agricultural experiment stations have 

 devoted much attention to these subjects and have made many deter- 

 minations of the digestibility of different foods by various animals. 



Recently in addition to proximate analyses of the food and feces and 

 determinations of nitrogen in the urine, calorimetric experiments have 

 been undertaken, and the balance of income and outgo of energy 



