2 BULLETIN 310, TJ. S. DEPABTMENT OF AGEICULTTJBE. 



ruined it lias not been possible to correlate melting point with digesti- 

 bility in an exact way on the basis of experiments hitherto made. 



The practical importance of further investigations on the subject is 

 indicated by the fact that the common domestic practices in the use 

 of fats, as of other food materials, is at present based very largely on 

 empirical knowledge, and quality in the resultant product depends 

 more upon experience and acquired skill than it does upon knowledge 

 of the physical and chemical properties of the ingredients used and 

 of their relation to the desired object. Yet it is obvious that the 

 whole matter is one which can not be definitely understood, stand- 

 ardized, and controlled unless such knowledge is available. A full 

 understanding of the materials, of the nature of household methods 

 of handling them, and of the resulting effects is necessary as a basis 

 for real economy as well as for more rational and satisfactory use of 

 foodstuffs. The right use of food materials must be governed also 

 by a knowledge of their digestibility and their value as sources of 

 energy available to the body. Neither can one overlook the modi- 

 fications which are due to the combination of ingredients into foods 

 and to the combination of foods to form meals. 



It seemed desirable, therefore, from both the scientific and the 

 practical standpoint to study the digestibility of the more common 

 culinary and table fats prepared in a comparable manner and incor- 

 porated in a uniform basal ration. It was with this idea in mind 

 that the digestion experiments with four of the more common animal 

 fats reported in this bulletin were undertaken. These experiments 

 form part of an extended study of the food value and household 

 uses of animal and vegetable fats of different sorts, having to do with 

 (1) the thoroughness of digestion of the fats, (2) the specific dynamic 

 effect of a diet rich in fats of different kinds, (3) the relation of 

 the available (net) to the total (gross) energy values of fats, and (4) 

 the relation of domestic ways of using fat to the quality of foods. 



NATURE OF THE DIET. 



The experiments here reported were made with beef tallow, mutton 

 tallow, lard, and butter, which were purchased in the open market. 

 The butter was a good commercial grade and was used as purchased. 



The beef, mutton, and pork fats were kidney fats. A fairly large 

 quantity of each was rendered in the laboratory in order to provide 

 uniform material for use in each series of experiments. The fat was 

 cut into small pieces, freed from any noticeable muscular tissue, and 

 finely ground in a meat cutter such as is used in the home. It was 

 then rendered in a double boiler, when it was found that the fat sep- 

 arated readily from the inclosing tissues (the temperature during 

 rendering did not quite reach 100° C). The fat was finally strained 

 through medium fine huckaback and heated, but not much above 



