AND OF PRODUCTS OF METABOLISM. 293 



the bottom line of the table we see that, 58 days after 

 the beginning of the experiment, none of the 50 tad- 

 poles fed 011 plants and on liquid egg albumen were sur- 

 viving; but of those fed on fish and on beef, respect- 

 ively 48 and 66 per cent, were alive, and had under- 

 gone their metamorphosis into frogs. 



The effects of certain foods on the plumage of birds 

 is well known to bird fanciers. Thus hemp seed causes 

 bull-finches and certain other birds to become black. 

 Cayenne pepper, mixed with the food 2 changes the yel- 

 low colour to an orange red. This colour change can 

 only be effected by feeding the very young birds; with 

 adults there is no effect whatever. Sauermann * found 

 that all races are not equally susceptible to the abnor- 

 mal diet, some being changed to a crimson, others to a 

 beautiful orange, whilst others remain absolutely un- 

 affected. He found also that canaries are not alone in 

 their susceptibility, for on feeding some white Italian 

 fowls, eight weeks old, with the pepper, orange stripes 

 appeared on the breast feathers of one of them after 

 ten days. Later on, the whole body was covered with 

 mixed white and orange feathers, and the breast had be- 

 come red. One other fowl also developed a red breast, 

 but the remaining ten showed no change whatever. 

 The doses of Cayenne pepper given were enormous (50 

 gm. daily), so that the conditions were absolutely un- 

 natural. 



More remarkable than these observations are the 

 facts ascertained by A. K. Wallace, and communicated 

 by him to Darwin, f Thus he states that " the natives 



* Archiv f. Anatomic u. physiol. Physiol. Abtheil., p. 543, 1889. 

 f " Animals and Plants," ii. p. 269. 



