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that serves to build tissue and carry' on the life processes of the animal 

 body. Therefore, to carry on the comparative study of the nutritive value 

 of these foods further we determined the digestibility, or, as Dr. Atwater 

 prefers terming it, the availability of the various food constituents con- 

 tained in them. 



Practical experiments of this nature are surrounded by many diffi- 

 culties which it is not necessary to fully discuss at this time. Suffice it 

 to say that the necessity of having a large number of results to offset indi- 

 viduality, the separation of the feces, and the arranging of a diet that is 

 simple enough for the purpose of the experiment, and, at the same time, 

 palatable, are among the chief difficulties in procuring reliable results. 

 With reference to the last point, it may be stated that it is seldom possible 

 to have the experiment conducted with the single food under investiga- 

 tion, for the flow of digestive juices is somewhat influenced by the degree 

 with which the food is relished. A special food, such as any of those being 

 studied, if eaten day after day alone, may become so distasteful to the 

 subject of the experiment as to seriously interfere with normal digestion, 

 or even to prevent the completion of the feeding period. On the other 

 hand, while it is necessary to make the diet palatable, it must be simple 

 in order that the digestibility of the specific food under investigation may 

 be calculated. With the foods we studied, the addition of cream and 

 sugar, the digestibility of which are known, was sufficient to make the 

 diet palatable for the full period of the experiment. 



In carrying out our digestion experiments, healthy young men of 

 regular habits and taking a fair amount of exercise were used as subjects. 

 They were interested in the experiments and volunteered for the work, 

 and, consequently, willingly co-operated in every way to make the results 

 accurate and the experiments a success. The feeding period in all the 

 experiments was four days, and to offset the question of individuality, 

 each experiment was conducted in triplicate. 



Briefly, a general outline of the plan of the experiments is as follows : 

 A definite weight of the food under investigation was cooked ; from this 

 each man was allowed to take as much as he wished, an accurate account 

 being kept of the quantity taken, and at the end of the meal the remaining 

 portion was weighed. From the weight of the dry meal taken and its 

 weight when cooked and the weight of the portion eaten, it was possible 

 to calculate the weight of the original meal eaten by each man at each 

 meal, and, consequently, for all the meals throughout the four days of the 

 experiment. Care was taken to have the porridge for each meal cooked 

 alike, the time allowed for this purpose in all experiments, excepting some 

 which will be mentioned later, was 20 minutes from the time the bubbling 

 commenced. Each subject was allowed to use sugar and cream, of known 

 composition, to suit his taste, but an accurate account was kept of the 

 amount consumed. Knowing the composition of the meal, sugar, and 

 cream, and the weight of each used, it was possible to calculate the weight 

 of each constituent consumed. Before the first and after the last meal of 



