442 CLASS REPTILIA. 



frog- spawn may be usefully employed in external inflamma- 

 tions, as soothing and emollient. 



In the old pharmacopeia, oil of frogs is mentioned, which 

 is now generally abandoned, even by the empirics of the 

 continent. A plaster composed of these animals was the 

 invention of a French surgeon, Jean de Vrigo. But while 

 we smile at the errors committed by our predecessors in 

 the art of healing, we should not forget that the discovery 

 of the most efficacious remedies has been owing to accidental 

 experiment, and not to any speculative reasoning on the 

 economy of the human system. We should also remember 

 that no satisfactory account can even yet be given of the 

 modus operandi of such remedies ; and those who have rea- 

 soned from the fact of their being general or partial stimuli, 

 and, in consequence, made experiment of corresponding 

 stimuli, have failed in producing the same results. No one 

 can yet tell why sulphur should cure the itch, and why other 

 agents on the skin should not succeed equally well in remov- 

 ing that troublesome disease .•; and the same is true of the 

 exhibition of mercury in syphilis. 



Klein, who separated the frogs from the toads, has de- 

 scribed some foreign species, as have also Seba and Catesby. 

 Linnaeus but little extended the catalogue of this genus com- 

 paratively with the moderns. Latreille, in his Natural History 

 of Reptiles, has enumerated a dozen genuine ranae, and Dau- 

 din has at least doubled the number. 



We shall now cast a rapid glance over the more remark- 

 able species of this genus. 



The green frog^ {rana esculenta,) is called by our Gallic 

 neighbours the common frog. It is about two or three 

 inches long, without reckoning the hinder feet. It is found 

 abundantly in stagnant waters both in Europe and Asia? 

 though it is much less common in England than the rana 



