64 



says Dr Mayhow, you will perceive the corculum or 

 heart to pulsate, or to languish and cease from mo- 

 tion *. The hearts of frogs, reduced to torpidity, 

 were removed by Spallanzani, and living action 

 could still be excited in them, by the re-application 

 of a proper degree of heat : and the heart of a turtle, 

 on being put into milk-warm water, was repeatedly- 

 observed by Dr Gardiner to yield a tremulous mo- 

 tion, six or seven hours after it was removed from 

 the body, and had become much shrivelled and 

 dried. If suffered to become cold, it was insensible 

 to every stimulus ; but when again warmed in wa- 

 ter, it repeated its palpitations on being pricked with 

 a needle f These and many other facts which 

 might be adduced, sufficiently establish the necessary 

 concurrence of heat to the production of action in 

 animals : and prove likewise, that its abstraction, 

 although causing a suspension of the animal functions, 

 does not necessarily destroy the capacity of their re- 

 newal. 



50. The direct effects of light in producing the vari- 

 ous colours of vegetables (25.) have been distinctly 

 proved : and the experiments and observations of 

 Mr Davy, go to shew that this agent exerts a simi- 

 lar operation on the various classes of animal beings. 

 He has observed, that the zoophyta exposed to light, 

 are uniformly brighter coloured than those which 

 have by any means been secluded from it ; and he 

 succeeded in altering the colour of two sea anemones 



* Tractat. Quinq. p. 325. An. 1674. 

 j- On the Animal (Economy, p. 4 ft. 



