DIGESTIVE ENZYMES IN POIKILOTHERMAL, VERTEBRATES 189 
In the carp the rate of tryptic digestion for a given amount of hepatopancreas 
was low as compared with that in the true pancreas, such as is found in Necturus, 
turtle, or dog. However, if the relative size of the hepatopancreas is taken into 
consideration, this organ would probably contain an even greater amount of trypsin 
for the size of the animal than does a typical pancreas in other animals. The pan- 
creas of the pickerel, like that in many other teleosts, is a diffused organ, so that the 
pancreatic tissue used was more or less mixed with fatty and connective tissue. 
The well-defined pancreas in the amphibians and reptiles studied gave a high rate 
of tryptic activity. Since the amount of pancreas available from bull snakes and 
Necturus was very small, it was necessary to use less than half the proportion of 
tissue in the digests for them. Considering the comparatively rapid rate of amino 
acid and tyrosine production in the pancreatic digests of these two animals, it is 
probable that the capacity of a given weight of pancreas in the bull snake and 
Necturus for tryptic digestion is equal to that of the turtles and the dog. 
From Table 4, showing the results of parallel experiments at room temperature 
and at 37° C, it may be seen that tryptic digestion was much more rapid at 37° 
than at 23° C. for all the animals tested. The higher temperature seemed to produce 
a slightly greater rate of increase in tryptic digestion in the carp than in Necturus 
and the dog. 
Experiments were carried on in the same way as with the pancreas, using 
extracts of mucosa from different regions of the digestive tract to find out whether 
or not trypsin is secreted in other organs than the pancreas. No tryptic digestion 
was obtained in extracts from the stomach mucosa of various animals, including 
the pickerel, white bass, Necturus, and snapping turtle, nor from the intestinal 
mucosa of Necturus, turtle, bull snake, and dog. There was slight evidence of 
tryptic digestion (increase in tyrosine and amino acid) in the intestine of the pickerel 
and in the caeca of the crappie. Repeated experiments using extracts from the 
mucosa of the anterior, middle, and posterior regions of the alimentary tract of 
the carp all showed no increase in amino acid or tyrosine in 8 days. Bile from the 
carp also produced no digestion of coagulated egg albumin in digests at a pH of 
approximately 8.4, 7, and 3. Homburger (1877, cited by Biedermann), however, 
reported that in carp aqueous extracts of hepatopancreas, intestinal mucosa, and 
bile itself digested fibrin in neutral or alkaline but not in acid solution. E[rukenberg 
in the same year (1877, cited by Biedermann) reported the indubitable existence of 
trypsin formation in the intestinal mucosa of many teleosts and especially in the 
carp. If true trypsin were secreted in the intestinal mucosa of the carp, digests 
made up in exactly the same way as those which show strong tryptic digestion for 
the pancreas should likewise produce tyrosine and amino acid. In the pickerel, 
where some tryptic digestion by intestinal mucosa extracts was observed, the 
amount of amino acid and tyrosine was exceedingly small as compared with diges- 
tion by the pancreatic extracts. It seems probable, therefore, that the intestinal 
mucosa plays no part of digestive importance in the secretion of trypsin in animals 
having a well-defined pancreas, and that in fishes with a difi^used pancreas a trace 
of tryptic digestion by extracts from the intestinal wall may be due to small ramifica- 
tions of pancreatic tissue embedded within the wall. 
