1008 EXPERIMENT STATION RECORD. 



body would live most economically. It is, however, not certain that 

 the best combination of nutrients (protein and nitrogen-free material) 

 has been found and is shown by the feeding standards. For instance, 

 if the ration contains a very large quantity of nitrogen and practically 

 all is excreted in the urine and feces it may be fairly considered as 

 wasteful unless it can be shown that the gains made are enough better 

 to offset the cost of such a ration, for nitrogen is without doubt the 

 expensive nutrient. By better gains is meant that the material gained 

 consists of lean rather than fat, or that the fat and lean are better dis- 

 tributed. Muscle, i. c, lean, contains about 23 per cent of protein 

 (nitrogen multiplied by 6.25) and by this factor the amount of lean may 

 be computed approximately from the gain of nitrogen. 



The small gains of nitrogen which are observed in many experi- 

 ments and which may be due to a variety of causes are often found to 

 be counterbalanced by corresponding losses if the period of observa- 

 tion is long continued. In order that there should be a gain of muscu- 

 lar tissue, of importance from the standpoint of feeding animals for 

 profit, there should be a regular and constant gain of nitrogen of con- 

 siderable amount. It has been claimed that by special methods of 

 feeding it is possible to cause very considerable increase of gains in 

 muscular tissue. The results of experiments which have been con- 

 ducted on this line are, however, contradictory. It is not improbable 

 that a system of feeding followed from birth may materially affect the 

 body structure of an animal. Until further observations are made 

 definite statements concerning this question are not warranted. 



It is undoubtedly true that different methods of feeding influence 

 the way in which fat is accumulated in the body. It has been claimed 

 tli at if animals are fattened quickly the fat will accumulate in large 

 masses in certain localities, whereas if the fattening period is of long 

 duration and the fat is accumulated slowly it will be distributed 

 throughout the carcass. The best methods of feeding and the most 

 suitable rations for securing well-distributed fat and lean are not 

 known with certainty. The conditions which inliuence the constant 

 gain of nitrogen (if this is possible) and hence the gain of lean are 

 not well understood. A consideration of the problem of feeding for 

 lean (whether this be understood to mean feeding so as to insure a 

 better distribution of lean and fat in the carcass or a total gain in 

 muscular tissue) affords one of the most useful investigations in con- 

 nection with feeding experiments. 



As previously stated, determining the gain or loss of nitrogen fur- 

 nishes data for computing the gain or loss of lean. If it were not for 

 variation in water content of the body as well as in the contents of 

 the alimentary canal the gain or loss of fatty tissue would be shown 

 by subtracting the gain or loss of lean from the total gain or loss, 

 since it is assumed that fat is the only nitrogen-free substance gained 

 in any considerable quantity. 



