40 History of physical Science from [July, 



ment except water. The animals swallowed the food with 

 avidity ; but they gradually became thin, and in about six weeks 

 died of starvation. An ulcer always broke out in the cornea of 

 the eyes, and they lost their sight some days before their death. 

 The same experiments were repeated on other dogs, substituting 

 gum and butter for sugar. The result in both cases was exactly 

 the same. From these experiments, M. Magendie drew as a 

 conclusion that food destitute of azote is incapable of nourishing 

 dogs. — (Ann. de Chim. et de Phys. hi. 66.) 



These experiments are of so decisive a nature that they seem 

 at first sight perfectly conclusive. There is one circumstance, 

 however, which would render it desirable that the experiments 

 should be repeated in a somewhat different manner — I allude to 

 the great influence of habit upon the digestive powers of animals. 

 It is possible that the stomach of dogs may not be capable at 

 once of digesting food so different from what these animals are 

 accustomed to, as sugar, gum, and butter. But if the change of 

 food were brought about gradually, and not all at once, is it not 

 probable that dogs might be made to live upon sugar, gum, and 

 even butter ? A sheep is accustomed to live upon vegetable food, 

 and it is incapable at first of digesting animal food ; but it may 

 be brought by degrees to relish animal food, and even to live on 

 it. It is said that in such cases the animal becomes incapable 

 of digesting vegetable food. This effect of habit renders it very 

 difficult to draw unexceptionable consequences from experiments 

 on living animals. 



2. Composition of Animal Substances. — Gerard has subjected 

 several animal substances to analysis by heating them in a glass 

 tube previously mixed with peroxide of copper, 

 table exhibits their constituents as then obtained 



The following 



Urate of barytes he found composed of 



Uric acjd 61-64 100-00 15-667 



Barytes 38-36 62-23 9-75 



100-00 



