Miscellaneous. 



439 



I am not aware of any experiments which shew, how much carbonic 

 acid may be in water without being detrimental to the life of marine 

 animals; but certain it is, that the luxuriant vegetations which 

 analogy leads us to believe must have existed in the sea at this 

 period, would extract carbonic acid from, and furnish oxygen to the 

 surrounding water. 



The amphibians require very little oxygen for the support of their 

 vital functions. Frogs will live for four or six hours in an atmos- 

 phere of pure hydrogen or nitrogen, which does not contain a particle 

 of oxygen. And although the amphibians require less oxygen than 

 the terrestrial saurians, still we find that the economy of the latter re- 

 quires much less oxygen than that of higher animals. Their lungs are 

 therefore, comparatively imperfect, and the two systems of circu- 

 lation incomplete ; for their arteries circulate a mixture of venous 

 and arterial blood. I do not know if there are any experiments on 

 record, of the powers of any particular saurian to live in an atmos- 

 phere deficient in oxygen and surcharged with carbonic acid, such 

 as we suppose existed during " the age of reptiles." I hoped to 

 have been able to shew you some experiments of their power to do 

 so ; but from their general torpidity at present, I have not been able 

 to meet with any lizards to secure for this purpose. In a few 

 weeks, however, they will be coming out of their holes, and I shall 

 introduce them into an atmosphere of the olden times, such as their 

 progenitors revelled in when they were masters of the world, and 

 multiplied themselves to such an amazing extent. 



All reptiles are distinguished by the small amount of food which 

 they consume, and by their tenacity of life under very trying cir- 

 cumstances. The food which they do take is not of a nature to be 

 transformed into carbonic acid; nor are their organs of respiration 

 suited for this transformation, even if it were. Hence it is, that they 

 do not require much oxygen for the support of their respiratory 

 functions, and that they expire so little carbonic acid. Hence it is 

 also, that they depend upon the warmth of the air to keep up the 

 temperature of their bodies, having no means of generating heat 

 within. Considering then these facts, and the supposed nature of 

 the atmosphere during this period, we discover a sufficient cause 

 why this should have been (as Mr. Mantell aptly denominates it) 

 « an age of reptiles ;"— they did not require much oxygen, which 

 the air could not have afforded. Their respiratory functions were 

 not retarded by an excess of carbonic acid, which would have 

 proved fatal to animals of a higher organization ; nor did they 



