6 DEPARTMENT BULLETIN 1492, IT. S. DEPT. OP AGRICULTURE 
effects of that feed on firmness under various conditions, and to de- 
termine the requirements for hardening peanut-fed hogs on different 
hardening feeds. While work along these lines has been continued, 
it was soon found necessary to investigate other feeds, as well as 
factors aside from feed. Among the other feeds which called for 
study on account of their probable softening influence were rice 
polish, rice bran, mast, and soy beans. The other factors which early 
showed their possible influence were initial weight, rate of gain, 
finish, sex, thrift, previous treatment, and breed. Thus the scope of 
the work was greatly broadened. Certain conclusions have been 
reached and published with the data supporting them. Specific 
reference will be made to those results at appropriate points in this 
bulletin. 
RELATION OF COMPOSITION OF FAT TO FIRMNESS OF CARCASS 
The firmness of the carcass is in large measure determined by the 
firmness of the adipose tissues and this in turn by the composition of 
the fat contained in these tissues. Analyses of the fat have shown 
that increasing unsaturation of the fat is accompanied by increasing 
softness of the carcass. It has therefore seemed desirable to determine 
the relationship between the committee grades and the composition 
of the fat. From this information one may be interpreted in terms 
of the other, and the data from both sources taken together give 
added exactness to the experimental results. 
Both methods of evaluating firmness have proved their usefulness 
throughout the investigations. The physical grading of the carcass, 
according to recognized commercial standards, is a very practical 
means of classification from the marketing standpoint. The data 
on the composition of the fat when in terms of such fat constants as 
the iodine number or refractive index give a general but reliable 
knowledge of the composition, while the more detailed and more 
difficult analysis for the content of the several fatty acids gives a 
deeper insight into the fundamental character of the effects of feeds 
and other factors on fat formation. This section of the bulletin is 
concerned principally with the comparison of refractive index and 
iodine values to the committee grades and is based on the results of 
those experiments which have been summarized in Department Bul- 
letin 1407 (4) 4 as well as in this bulletin. 
As would be expected in a study of this sort, where two such 
widely different methods are used, there have been numerous diver- 
gent results between laboratory tests and committee gradings. In 
some cases the laboratory test has failed to indicate the degree of 
softness ; in others the committee grading has been at fault. Numer- 
ous factors affect the results, many of which are not well understood. 
The data on refractive index as well as iodine numbers have been 
summarized according to feeds and feed combinations, since it was 
found that standards of firmness as determined by laboratory tests 
varied with the rations fed. These variations have been ascribed 
largely to the variations in the amount and the degree of unsatura- 
tion of the feed fat. 
Soft lard ordinarily contains a greater amount of unsaturated, or 
liquid, fatty acids than hard lard. However, the proportions as well 
4 Italic numbers in parentheses refer to " Literature cited," p. 50. 
