METABOLISM. 33 
of good quality, the fat having a melting-point and iodine number 
not widely different from those obtained with the most approved 
rations. While it is possible that part of this effect was due to a 
reduced consumption of maize oil, so that more fat was produced 
from the other ingredients of the food, the conclusion seems justified 
that the principal factor was the influence of the skim milk upon 
the nutrition of the fat cells. This influence may with some degree 
of probability be ascribed to its protein, and it is worthy of notice 
that in Shutt’s experiments the rations which produced the highest 
grade of pork were composed of materials rich in protein. 
Another fact warns us to be cautious in our interpretation of 
the results of this class of feeding experiments. Such experiments 
in most cases involve a comparison of the composition of the fat 
from animals differently fed. Albert * has found that both with 
swine and sheep the composition of the body fat is subject to very 
considerable individual variations as to melting-point, refractive 
index, and iodine number, the differences being, in his experiments, 
greater than the average differences which could be ascribed to the 
feeding. 
Moreover, the fat of the same individual has not the same com- 
position in different parts of the body. This point has recently 
been the subject of an elaborate investigation by Henriques & 
Hansen,} whose results show a higher melting-point and a lower 
iodine number in the inner as compared with the outer layers of 
fat. This difference they ascribe to the difference in the tempera- 
ture of the tissues and support this view by an experiment with 
three pigs. One animal was kept in a stall heated to about 30° C. 
for two months, while the others were exposed to a temperature of 
0° C., one unprotected and the other partially enveloped in a sheep- 
pelt. At the close of the experiment the fat immediately under 
the skin gave the following figures: 
Iodine Solidifying 
Number. Point. 
Kept at 30°-35° C........-.--4- 69.4 24.6° C. 
Kept at 0°, in sheep pelt: 
Part under the pelt........ 67.0 25.4° C. 
Part exposed...... 0 .....05. 69.4 24.1° C. 
Kept at 0°, unprotected........ 72.3 23.3° C. 
* Landw. Jahrb., 28, 961, 986. 
+ Bied. Centr. Blatt. Ag. Ch., 30, 182. 
Digitized by Microsoft® 
