MANUAL OF NATURAL HISTORY. 3 



and inapplicable. Another distinguishing feature 

 was believed to be afforded by burning the sub- 

 stance in question, when, if of an animal nature, 

 it would give out an empyreumatic odour, because 

 of its containing nitrogen ; but it has since been 

 shewn that this element is also afforded by vege- 

 tables. The most satisfactory definition yet advanc- 

 ed is, that "animals are possessed of an internal 

 receptacle for food, wherein they collect the nutri- 

 ment destined for their support/' * Even this, how- 

 ever, is not fully correct. Another line of demar- 

 cation has been attempted to be drawn from the 

 circumstance that animals obtain nutriment only 

 from previously organized matter, while plants ar 

 nourished by inorganic material, which they thus 

 prepare for the ultimate support of animal life. 

 Many, if not all of these hold good, and are quite 

 applicable in reference to the more advanced forms 

 of both kingdoms; but in their primary stages the 

 question still remains to be solved. It , has been 

 beautifully observed by an eminent zoological autho- 

 rity, " Light and darkness are distinct from each 

 other, and no one possessed of eye-sight would be in 

 danger of confounding night with day ; yet he who, 

 looking upon the evening sky, would attempt to 

 point out precisely the line of separation between 

 the parting day and the approaching night, would 

 have a difficult task to perform." And so it is with 

 the point we have had under consideration. Nature 



* Vide " Rymer Jones." Nat. Hist, of Animals. Vol. I., p. 5. 



B2 



