186 BULLETIN OF THE BUKEAU OF FISHEEIES 
by itself later. Individual variations among different animals of the same species 
were not great. With the exception of the carp, also, there seems to be little 
change in the rate of peptic digestion correlated with differences in food habits. 
Among the fishes the pickerel, which feeds almost entirely upon fishes, does not 
show an outstandingly higher rate of peptic digestion than the bluegill and crappie, 
the diet of which includes a larger proportion of vegetable matter, more insects, 
and small crustaceans. In 18 bluegUls examined Pearse (1921) found that plants 
and algse constituted 24 per cent of the total volume of food in the digestive tracts. 
Coagulated egg albumin seems to be equally well digested by the enzymes of 
fish, amphibians, reptiles, and mammals. Several workers, however, have re- 
ported that coagulated egg albumin is only very slowly digested by fish pepsin 
(Decker, 1887, for pike, cited by Biedermann; Yung, 1899, for selachians; and 
Bodansky and Rose, 1922). Bodansky and Rose (1922) stated that the slow 
digestion of coagulated egg albumin by fish pepsin was not entirely due to the 
smaU surface exposed, for finely divided albumin was not digested with an ap- 
preciably greater rapidity. "Furthermore, a commercial pepsin solution capable 
of producing an effect on fish meat similar in extent to that exerted by fish pepsin 
digested coagulated egg albumin quite readily." Their criterion for the extent of 
digestion of the coagulated egg albumin, or just how finely the egg albumin was 
divided, was not stated. Obviously a comparison between the activity of extracts 
of gastric mucosa and the activity of commercial pepsin would not be as satisfactory 
as the comparison between the activity of uniformly prepared extracts from the 
gastric mucosa of the animals. 
The only previous attempt to compare the rate of digestion in representatives 
of different classes of poikilothermal vertebrates is that of Riddle (1909), who tried 
to determine the rate of gastric digestion in living fishes, amphibians, and reptUes 
by comparing the rate of disappearance of coagulated egg white in Mett's tubes 
introduced into the stomach. Riddle concluded that there was a progressive loss 
in digestive power in ascending the vertebrate scale from fishes to reptUes. How- 
ever, in view of the extremely wide differences which Riddle obtained in the same 
species under the same conditions, and the lack of fairly constant results for each 
class of animals studied, such a conclusion seems highly speculative, and the method 
used an unsatisfactory one for reliable comparisons. The results obtained in the 
present investigation definitely show that in evolution from fishes to reptiles there 
has been no loss in digestive power. On the contrary, the digestive power in the 
reptiles used, if different, seems to be a trifle greater than in other groups. The 
results in Table 1 indicate that in poikilothermal vertebrates with well-developed 
stomachs and in the dog ^ equal amounts of stomach mucosa possess approximately 
the same digestive power. 
The carp, from which outstandingly different results were obtained, differs 
in anatomical structure from fishes of other groups in the absence of a glandular 
stomach and in the presence of an extensive hepatopancreas. The bile duct enters 
the alimentary tract immediately behind the pharynx, and the entire alimentary 
canal, which is about 4 feet in length in a carp weighing 2 kilograms, has the appear- 
ance and histological structure of an intestine. It is wholly devoid of gastric 
glands (Oppel, 1897). 
1 In preparing the extract from gastric mucosa of the dog a larger proportion of the pyloric region than of the cardiac region 
was used, which may account for the slightly lower rate of tyrosine production in this animal. 
