THE DIGESTIVE TRACT OF ELASMOBRANCHS. 13 
lobsters fed to the fish could not be found in the stomach after four days of digestion, 
the question arose as to whether the dogtish actually does digest chitin. I therefore 
began, during this summer, a physiological study of the alimentary canal of J/uste/us 
canis. During the summers of 1905 and 1906 the investigation was extended to 
include Carcharias littoralis, Squalus acanthias, Tetronarce occidentalis, Carcharhinus 
OLSCUTUS, Raja erinaceds Lamna cornubica, and Dasyatis centrura. The work con- 
sisted of — 
(a) The preparation, for artificial digestion, of extracts of buceal, esophageal, 
and gastric mucous membranes. 
(b) The study of the normal content of the stomach. 
(c) The study of the acidity of the stomach. 
(d) Determining whether or not J/ustelus canis digests chitin. 
(e) The preparation of extracts of the intestinal mucous membrane and of the 
pancreas. 
({) The study of the activation of the pancreas. 
(g) The study of the rectal gland. 
BUCCAL CAVITY. 
The elasmobranchs as a rule swallow their food whole, without mastication. 
Naturally we should suppose that little digestion goes on in the buccal cavity. This 
probability is increased by the absence of glands. Since Krukenberg (1877) claimed, 
however, that the buccal mucus of some fish, especially of Cyprinus carpio and 
Lophius piscatorius, possesses a diastatic action, it seemed proper to test the action 
of various kinds of infusions of the buccal mucous membranes of selachians. 
The buccal cavity of a number of these fish, freshly killed, was scraped. The 
mucus thus collected was white in color, neutral in reaction, and gave a good test for 
mucin, but showed no diastatic activity. Scrapings of the buccal cayity of all the 
elasmobranchs obtainable gave the same results. 
The buecal cavity of elasmobranchs, then, as Yung has already shown for 
Seyllium canicula, secretes mucin comparable to that of the saliva of man, but with 
no diastase. 
Water extracts of the buccal mucous membrane have no permanent emulsifying 
action on olive oil. 
Five-tenths per cent hydrochloric acid extracts of the buccal mucous membrane 
filtered free of mucin have no peptonizing action on white of egg or pig fibrin. The 
buecal mucous membrane then contains no pepsin-like enzyme. 
Conclusions: The buccal mucus of all the elasmobranchs examined contains 
mucin but no digestive ferment. ; 
ISOPHAGUS. 
The reaction of the esophagus of a fasting fish is neutral. Tested when the 
fish is in full digestion, on the other hand, the reaction of the esophagus is acid, 
due, undoubtedly, to regurgitation from the stomach. 
Mucus was scraped from the esophagus of ten fasting smooth dogfish. This 
mass was divided into two equal portions and one portion was made slightly alkaline 
with sodium carbonate, while the other was acidified to the extent of five parts of 
