AND OF PRODUCTS OF METABOLISM. 295 



this was so, at least in part. The observations which 

 have been made from time to time as to the effects of 

 various kinds of food on the thickness of the stomach 

 wall, are, however, free from all such doubt. The 

 change produced must evidently be the direct result of 

 the altered diet. Thus John Hunter observed a most 

 marked thickening and hardening in the stomach of a 

 gull (Larus tridactylus) which had been fed for a year 

 on grain. It is stated by Dr. Edmondston that a similar 

 change takes place under natural conditions every year 

 in the stomach of the common Herring gull (Larus 

 argeniatus). Thus in the Shetland Islands this bird 

 feeds in the winter on fish, but in the summer fre- 

 quents the cornfields and feeds on grain. Dr. Edmond- 

 ston has also noticed a somewhat similar change in the 

 stomach of a raven which had been fed for a long time 

 on vegetable food. Again, Menetries found that in an 

 owl (Strix grallaria) the effect of vegetable diet was to 

 change the form of the stomach, and make the inner 

 coat leathery.* 



The converse experiment of feeding graminivorous 

 birds on a flesh diet has been made by Dr. Holmgren. 

 By feeding pigeons on meat for a considerable time, he 

 found that the gizzard gradually acquired the qualities 

 of a carnivorous stomach. Again, Delage f fed a fowl 

 for three years on meat, and found that the muscular 

 substance of its gizzard was considerably decreased. 

 All these results, though apparently so unequivocal, 

 have not passed unchallenged; for G. Brandes,J who 



* Vide " Animals and Plants," ii. p. 292. 

 f L'Annee Biologique, 1896, p. 468. 

 j: Biol. Centralblatt, xvi. p. 825. 



