1891.] Processes of Ammocoetes. 253 



We may consider for this purpose that the alimentary canal 

 consists of three portions, 1st the pharynx, 2nd the narrow tube or 

 anterior intestine which leads from the pharynx to the mid-gut 

 and terminates posteriorly at the entrance of the bile-duct where 

 the sudden enlargement of the alimentary tube marks the begin- 

 ning of the 3rd portion, the intestine proper. The glandular 

 appendages in connection with these parts are, (1) the so-called 

 thyroid gland, with its duct opening into the pharynx, and (2) 

 the liver with its duct opening into the intestine. 



In order to test for the presence of digestive ferments, I made 

 extracts of the epithelium lining the pharynx, the liver, the intes- 

 tine and the thyroid in *2 °/ HC1. or in glycerine, using in each 

 experiment the organs of two or more Ammocoetes of Petromyzon 

 Planeri. I may here mention that I can confirm Krukenberg's 

 experiments on the digestive ferments in fishes and invertebrates 

 as to the temperature at which they are most active. I find my 

 extracts are very much more powerful at 38° to 40° C. than at 15° 

 to 20° C, many authors giving the lower temperature as that at 

 which the digestive extracts of fishes and cold-blooded animals 

 generally are most active. I found that all parts of the alimentary 

 canal, with the exception of the thyroid gland, were capable of 

 digesting fibrin in a 2 °/ HC1. medium with greater or less 

 rapidity. I used carmine-stained fibrin after Griitzner's method, 

 and always used as control experiment a *2 °/ o HC1. solution alone 

 and an extract of some tissue of the animal which was inactive in 

 digestion. 



The results of these experiments may be summed up as 

 follows : — The extract of the liver is always the most powerful ; — 

 thus in one case about 1 c.c. fibrin was entirely digested in from 

 2 to § hr. by an extract made from the livers of two Ammocoetes. 

 The epithelium of the pharynx comes next in activity, thus in the 

 case mentioned the epithelium of the pharynx of the same two 

 animals digested the same amount of fibrin in about 1^ hrs. Next 

 in order of activity comes the extract of the intestine ; this always 

 gives decided evidence of digestive power, but if carefully cleaned 

 out with a soft brush before the extract is made, so as to remove 

 as far as possible the secretion from the liver, then its power of 

 digestion is very far behind that of the pharynx or liver, although 

 in all cases digestive activity is still manifest. Finally the extract 

 of the thyroid is always inactive. 



So far I have not succeeded in obtaining any results in a 1 °/ 

 sodium carbonate medium, and conclude that tryptic ferment is 

 absent. In relation to this it is interesting that in a youno- 

 Selachian Krukenberg found that a tryptic ferment was entirely 

 wanting, and he suggests, for this and other reasons, that in primi- 

 tive vertebrates the digestion was rather peptic than tryptic. 



