MODIFYING EFFECTS OF FOOD. 69 



of a certain diet. The variations in the structure of the stomach 

 of birds experimentally proved by Hunter, Edmonstone, and 

 Holmgren, have only a superficial importance, since we do not 

 know whether modifications of other parts were connected with 

 them or might subsequently have originated from them. If 

 now we reflect that, in spite of the great general interest of the 

 experiments of Hunter and Holmgren, not the smallest additional 

 fact has been established experimentally since their time either 

 by modern zoology or, on the other hand, by organic physio- 

 logy no one having investigated the subject it may be 

 regarded as a not improbable opinion that experiments purposely 

 carried out on a large number of animals, as widely different as 

 possible, would offer a much greater mass of results than are at 

 present at our disposal. Moreover, it is not impossible that 

 change of food may lead to more fundamental modifications 

 in other animals than those in the stomachs of the pigeon and 

 herring-gull, since we know that different species react in 

 very various ways under identical influences. The above- 

 mentioned cases of the variations in external colouring pro- 

 duced by food in birds and butterflies sufficiently prove -this; 

 for there is a large number of animals in which a change of 

 food has no influence whatever on the skin-pigment. 



The conclusion of the investigation conducted in this chapter 

 is not very satisfactory : we have seen that with respect to the 

 direct modifying effects of food everything in fact remains to 

 be done. However, the few well-ascertained cases suffice to 

 prove that the smallness of our stock of positive knowledge on 

 the subject is probably due only to the fact that no systematically 

 pursued investigations have been carried out. 15 This may, it is 

 true, be excused on the score that zoologists on whom this 

 task would principally devolve, owing to the position taken up 

 by physiologists have been prevented fulfilling it partly by 

 the direction which the development of their science has taken, 

 but above all by the absolute insufficiency of their institutes 

 and laboratories. 



