8 BULLETIN OF THE BUREAU OF FISHERIES. 
The general tendency of Krukenberg’s studies, therefore, is to establish the 
existence of an evolution of the digestive function from the invertebrates (molluscs, 
crustacea, etc.) to the higher vertebrates. By the great variation in the distribution 
of the ferments, fish, according to him, show the principal stages of this evolution. 
Luchhau (1878), by means of glycerin extracts of the mucous membrane of the 
stomach of the salmon, pike, and sandre, secured juices that would peptonize fibrin. 
Contrary to Fick and Murisier (1873), he observed that the peptonizing action is 
more rapid at 40° C. than at 15° C.  Luchhau also examined the digestive activity 
of the juice of certain Cyprinidee (Cyprinus carpio, C. blicca, C. carassius, C. tinea, 
C. erythrophthalmus, and Abramis brama), which do not have a functional stomach. 
In no case did he find an enzyme digesting in an acid medium—that is, pepsin; but 
he did find that fibrin is digested by the neutral or alkaline extract of the intestinal 
mucous membrane and that the digestive power is greater at 40° C. than at lower 
temperatures. Luchhau compared the ferment of the intestines of Cyprinide to the 
trypsin of mammals, and in addition to the trypsin-like ferment he found the diastatiec 
ferment also. The trypsin-like ferment, he asserted, is secreted in the middle region, 
while the diastatic ferment is secreted along the whole length of the intestine. He 
did not find a fat-splitting ferment, nor, unlike Krukenberg, did he find any ferment 
which would digest albumen. 
In researches upon the composition of the gastric juice, Richet (1878) analyzed 
the gastric juice of different fishes. He proved conclusively the presence of hydro- 
chloric acid, free or combined with organic substances, such as tyrosin and leucin. 
He found the acidity to be high, in the case of Seyllium canicula even as high as 
1.5 per cent hydrochloric acid. The digestive power of Scyllium canicula he found 
to be greater than that of Lophius piscatorius. In a later paper Mourrut and 
Richet (1880) found that the liquid in the stomach lost its digestive power by filtra- 
tion. An acidity of 2.5 per cent was found by them to prevent peptonization, 
while moderate heat favored the action of the ferment. Mourrut and Richet did 
not observe that either Lophius or Scylliwm produced a diastatic ferment in the 
stomach. 
In a still later study of digestion in fish, Richet (1882) confirmed the facts 
previously given by him and declared that the gastric juice of sharks digests the 
chitin of crustacea. Further, the pancreas of Scyl/ium and of Galeus has no action 
on proteids but is limited to the transformation of starch to sugar and to the 
emulsification of oil. 
Raphael Blanchard (1882) investigated the rectal gland of elasmobranchs and 
the pyloric appendages of teleosts. He found that the former organ produces both 
a diastatic and a fat-splitting ferment. The pyloric appendages, according to this 
investigator (1883), represent, in a certain sense, the pancreas, since they secrete a 
diastatic enzyme and a trypsin-like enzyme. 
The presence of the trypsin-like ferment in the pyloric appendages has been 
proved also by W. Stirling (1884, 1885), who worked on the herring, cod, and hake, 
and made glycerin extracts of the stomach and pyloric appendages. In the stomach 
he found a ferment acting in acid and in the pyloric appendages one acting in an 
alkaline medium, from which observations he concluded that the stomach secretes 
pepsin, the pyloric appendages trypsin. 
