USES OF CARBON IN THEIR FOOD. 55 



ammonia. In like manner, the faeces in lions and 

 tigers are scanty and dry, consisting chiefly of bone 

 earth, with mere traces of compounds containing 

 carbon ; but their urine contains, not urate of am- 

 monia, but urea, a compound in which carbon and 

 nitrogen are to each other in the same ratio as in 

 neutral carbonate of ammonia. 



Assuming that their food (flesh, &c.) contains 

 carbon and nitrogen in the ratio of eight equivalents 

 to one, we find these elements in their urine in the 

 ratio of one equivalent to one ; a smaller proportion 

 of carbon, therefore, than in serpents, in which res- 

 piration is so much less active. 



The whole of the carbon and hydrogen which the 

 food of these animals contained, beyond the amount 

 which we find in their excrements, has disappeared, 

 in the process of respiration, as carbonic acid and 

 water. 



Had the animal food been burned in a furnace, 

 the change produced in it would only have differed 

 in the form of combination assumed by the nitrogen 

 from that which it underwent in the body of the 

 animal. The nitrogen would have appeared, with 

 part of the carbon and hydrogen, as carbonate of 

 ammonia, while the rest of the carbon and hydrogen 

 would have formed carbonic acid and water. The 

 incombustible parts would have taken the form of 

 ashes, and any part of the carbon unconsumed from 

 a deficiency of oxygen would have appeared as 

 soot, or lamp-black. Now the solid excrements are 



