1112 REPORT OF COMMISSIONER OF FISH AND FISHERIES, [4] 



Determination of the amount digested. — This can be accomplished by 

 either weighing the undigested residue, or by determining directly the 

 amount dissolved. In a recent work by Jessen^ on the influence of 

 different modes of preparation on the digestibility of meat, the former 

 method was used. Unless the amount of water contained in the meat 

 experimented with, however, is determined, a verj^ decided error may 

 be introduced. Thus Jessen found by experiment with frogs' legs^ 

 that 2 grams of the raw flesh, introduced into the stomach of a dog, 

 required on an average 4.46 hours for digestion, while the same 

 amount of beef, similarly prepared, required on an average 5.58 hours, 

 and thus from this experiment the relative digestibility of the two 

 would be as 84: 100. Our experiments, however, show quite a different 

 result, easily exi)lained by a determination of the percentage amount of 

 solid matter in the two kinds of flesh. Thus, while 20 grams of beef con- 

 tain on an average 5.1 grams of solid matter, the flesh of frogs' legs con- 

 tains but 3.5 grams. It is evident from this example, then, that a deter- 

 mination of the total solid matter is necessary in each species of flesh ; 

 but even when that is done, and corrections made accordingly we have 

 found a decided difliculty in filtering the digestive mixtures. The un- 

 dissolved residue of the fish is so gelatinous that it is next to an impos- 

 sibility to wash it entirely free from i)eptones. We therefore decided 

 to work with the filtrate, and after several trials by precipitating the 

 dissolved albumen with tannic acid, according to the method of John- 

 son,^ and also by determining the specific gravity of the fluid after filtra- 

 tion, we finally adopted the following method, which has proved quite sat- 

 isfactory. After the gastric juice has been allowed to act for the requisite 

 length of time on the 20 grams of flesh the mixture is cooled to 20° C, and 

 then diluted to 250 cubic centimeters, in a graduated flask, with distilled 

 water. After being thoroughly mixed it is filtered on a dry filter, and 

 then 50 cubic centimeters, or one-fifth of the entire mixture, is trans- 

 ferred by a pipette to a small weighed dish, and to it are added 5 cubic 

 centimeters of a standard solution of sodium carbonate of such strength 

 as exactly to neutralize the acid present. The fluid is then evaporated 

 to dryness on the water-bath, and finally dried at 110° C. until of con- 

 stant weight. In order that the results obtained may express the ab- 

 solute amounts of matter dissolved by the gastric juice, it is necessary 

 to carry on control experiments with the gastric juice itself. This is 

 also desirable as a ])roof of the uniform strength of the gastric juice. 

 Thus in each series of experiments 200 cubic centimeters of the standard 

 juice were warmed at 38° to 40° C. for 22 hours, so that all albumen con- 

 tained in the pepsin could be converted into peptone, then diluted to 

 250 cubic centimeters and 50 cubic centimeters, neutralized, evaporated, 

 and dried as already described. This residue, subtracted from the 



1 Zeiisclmft fiir Biologic, 19, 130. 



^md., p. 140. 



3 Bulletin de la Socielc chimique dc Paris, 2',), 40. 



