BULLETIN OF THE UNITED STATES FISH COMMISSION. 147 



the beginning tbc tail protrudes from the mouth, the head is, of course, 

 digested very soon ; but gradually there is some delay, as the digestive 

 liquids are only secreted in limited quantity, and the dissolved sub- 

 stances can be absorbed only gradually. Pike are not suitable for 

 making observations relative to the time occupied by digestion, as they 

 are in the habit of throwing up very soon some of the prey which they 

 have swallowed; but I have made experiments with perch and hake 

 which were fed on worms. 



A number of perch, measuring each about 15 centimeters [about 6 

 inches] in length, which had been kept on very short rations for some 

 time previous, were fed on worms, which they swallowed so greedily that 

 their bag-like stomachs were filled to their utmost capacity. In a perch 

 killed two hours later the food was found only in the stomach, the 

 gastric juices reacting in a strongly acid manner. After eight or ten 

 hours a portion of the worms had reached the front part of the intestinal 

 canal 5 but even after twenty or twenty-four hours the stomach was 

 still very full, while at the end of the intestinal canal balls of feces 

 were already forming ; after sixty or seventy hours the stomach was 

 empty ; and after one hundred and ten hours the front and middle i)arts 

 of the intestinal canal had likewise become empty, and only at the end 

 of the canal were there feces, and digestion might therefore be con- 

 sidered as finished. 



In hake which had been well fed with worms, they evenly filled the 

 entire intestinal canal from the throat to the anus after twelve or fifteen 

 hours; but owing to the stronger secretion of gastric juice in the front 

 I)art of the intestinal canal, they had been better digested there than 

 in the lower part. This explains the observation that half-digested 

 particles of food frequently protrude from the anus of fish, and from it 

 the conclusion may be drawn that if fish are to be fed with the view to 

 fatten them it is better to give them moderate quantities of food at * 

 frequent intervals, than to give them large quantities at longer inter 

 vals. 



The carp-like fish are frequently termed herbivorous fish, in contra 

 distinction to i)redaceous fish. This term, as I have been taught bj 

 numerous investigations, is entirely' erroneous. While young fish ol 

 all kinds, examined by me, were found to have eaten small crustaceans 

 and infusorians, the intestinal canal of all fish of the carp kind, meas- 

 uring more than a finger's length, always contained at all seasons larva? 

 of gnats, dragon-flies, day-flies, beetles, &c. 



Large quantities of iflants (green algaj) I found regularly only in the 

 intestinal canal of Gliondrostoma nasus ; but it remains to be examined 

 whether the algie or the large quantities of infusorians and other di- 

 minutive animals adhering to them, form the iirincipal food of this fish. 



Uncooked starch flour was not digested by any of the fish which I 

 examined. Even when, after being stirr<Ml with water, it was injected 

 into the intestinal can;d and lemained there for days, the extracts of 



