195 



smeared over with oil, lost, in the same time, only 

 45 grains. If also eggs be varnished over, or pla- 

 ced under the exhausted receiver, they do not cor- 

 rupt : and Bomare mentions the circumstance of 

 three eggs being found hi the wall of a church, 

 which, by being protected from the air, were quite 

 fresh after the lapse of 300 years *. These facts 

 prove, that a reciprocal action is going on at all 

 times between the carbon of the egg and the oxygen 

 gas of the air, by which carbonic acid is produced ; 

 but which action may, at any time, be interrupted, 

 either by closing the pores of the shell, or by ab- 

 stracting the pure part of the air. The loss of 

 weight which eggs suffer, arises, in all probability, 

 from the escape of their more watery parts, which 

 pass off through the processes of the chorion descri- 

 bed above ; and, as the same causes which obstruct 

 the exhalation of moisture, seem also to check the 

 emission of carbon, it is reasonable to suppose, that 

 they both proceed from the same individual struc- 

 ture. 



154. We have, in the next and last place, to in- 

 quire whence issues the carbon which unites with 

 the oxygen gas of the air to form carbonic acid, in 

 the respiration of man and other warm blooded ani- 

 mals. For the most part, this carbon has been sup- 

 posed to be derived from the venal blood, either in 

 the course of its transmission through the pulmona- 

 ry vessels of the lungs, or during its circulation 

 through the capillaries of the system: and to the 



* Encyclop. Brit. art. Physiology, 

 N 2 



