INVESTIGATIONS ON THE METABOLISM OF MILCH COWS. 805 



Boussingault called attention to the importance of the nitrogen con- 

 tent of feeding stuffs, and believed that this alone could be taken as a 

 basis for estimating their value. On the other hand, Haubner showed 

 that nitrogen-free material was useful for building up the animal body. 

 Nathusius showed that the woody fiber was to a certain extent injuri- 

 ous; and Boussingault finally modified his theory so that on the basis 

 of the nitrogen content feeding stuffs were divided into 4 classes: (1) 

 Hay and straw, (2) roots and tubers, (3) oil-bearing seeds, and (4) 

 grains, leguminous seeds, and oil cakes. 



The attempt was also made to compare feeding stuffs in a practical or 

 empirical manner by means of tables showing the so-called "hay 

 values," or the hay equivalent of different materials. Thus it was said 

 that 16§ kg. hay equivalent was required per 1,000 kg. live weight for 

 maintenance by cattle or sheep. IT the food supplied more than this, 

 each kilogram consumed in excess would produce a gain of 0.1 kg. body 

 material or fetus or 1 liter of milk. However, one hay differs from 

 another and other feeding stuffs also vary in composition, and as a result 

 there were soon a considerable number of "hay value" tables from 

 which it was impossible to select the correct one. An improvement was 

 suggested by E. Wolff, who took account of the chemical composition 

 of feeding stuffs and considered crude fiber as indigestible. Thus it 

 was said that normal hay should contain 8.2 per cent of protein, 41.3 

 per cent of soluble nitrogen-free material, and 30 per cent of crude fiber, 

 with a nutritive ratio of 1 : 5. This modification did not prove of much 

 value since crude fiber is partially digestible, and, further, the soluble 

 nutrients in different feeding stuffs have different nutritive values and 

 different digestibility. The convenient theory of hay values was there- 

 fore abandoned and experiments were undertaken with different kinds 

 of animals to learn how much protein, soluble nitrogen-free material, 

 and fat must be fed for different purposes. 



Grouven's normal feeding standards, which were published in 1862, 

 were determined by this method. They were a great improvement on 

 the tables of hay values, and superseded them. These standards were 

 a series of formulas based on experiments depending in part on the 

 general appearance of the subject, and on results of slaughter tests. 

 Grouven also made many investigations, including digestion and respi- 

 ration experiments, for the purpose of determining the nutritive value 

 of a number of simple nutritive materials, such as sugar, starch, and 

 dextrin. 



A curious theory was devised by Enzmann in I860. 1 He determined 

 the ratio of carbon to nitrogen in different feeding stuffs, designating 

 it the "specific carbon content," and on this basis arranged materials 

 as follows: Bice straw 117, potatoes 34, hay 27.4, red clover hay 17.4, 



1 Landw. Vers. Stat., 8 (1866), pp. 309, 320. For earlier work see Die Ernahrnng 

 der Organismen besomlers <los Mensclieu vrad der Tkiere iru hungerndeii Znstande. 

 Dresden: C. C. Meinhold & Soline, 1856. 



