638 THEORY OF INCUBATION. 



these particles. For it is self-evident, that what- 

 ever the organizing principle may be, it must 

 determine the composition and arrangement of 

 the molecules that form any part of the body, 

 modified, however, in an endless variety of ways 

 by surrounding circumstances. 



That caloric is the cause of sanguification, 

 would further appear from the fact, that it is the 

 obvious agent by which the eggs of birds, reptiles, 

 insects, fishes, and all other animals, are gradu- 

 ally changed from the state of a semi fluid germ, 

 into blood and the various organs of which they 

 are composed whether derived from the sun, by 

 which the lower animals are hatched from ordi- 

 nary combustion, as in artificial incubation, or 

 supplied by the natural temperature of the parent, 

 as in the ordinary process of hatching birds. Dr. 

 Theodore Schwann has shewn by a very careful 

 series of experiments, that when surrounded by 

 an artificial temperature at the proper standard, 

 the development of the egg can proceed to a cer- 

 tain extent without oxygen, while surrounded 

 with hydrogen or nitrogen, but not if exposed 

 to carbonic acid. And some recent experiments 

 of Mr. Towne, recorded in the fourth volume of 

 the Guy's Hospital Reports, were by many persons 

 thought to prove, that oxygen is not essential to 

 the early developement of the chick in ovo. For 

 he found that^after eggs w r ere surrounded with 

 strips of thin and dense paper, dipped in albu- 

 men, and then smeared over with varnish, the 



