AND INSENSIBLE PERSPIRATION. 6'5 



scarcely by any mechanical operation, or expansive pow- 

 er upon the fluids. The effect of heat is in proportion 

 to the degree of cold to which the plant has been accus- 

 tomed. In forced plants the irritability, or, to use the 

 words of a late ingenious author^-, who has applied this 

 principle very happily to the elucidation of the animal 

 ceconomy, excitability, is exhausted, as Mr. Knight 

 well remarks, and they require a stronger stimulus to 

 grow with vigour. See/>. 91. Hence vegetation goes 

 on better in the increasing heat of spring than in the de- 

 creasing heat of autumn. And here I cannot but oflfer, 

 by way of illustration, a remark on the theory advanced 

 by La Cepede, the able continuator of Buffon, relative 

 to serpents. That ingenious writer mentions, very tru- 

 ly, that these reptiles awake from their torpid state in 

 the spring, while a much less degree of heat exists in 

 the atmosphere than is perceptible in the autumn, when, 

 seemingly from the increasing cold, they become be- 

 numbed ; and he explains it by supposing a greater de- 

 gree of electricity in the air at the former season. Dr. 

 Brown's hypothesis, of their irritability being as it were 

 accumulated during winter, oflfcrs a much better solution, 

 either with respect to the animal or vegetable constitu- 

 tion. For the same reason, it is necessary to apply 

 warmth very slowly and carefully to persons frozen, or 

 even chilled only, by a more than usual degree of cold, 

 which renders them more susceptible of heat, and a tern- 

 perate diet and very moderate stimulants are most safe 



* Dr. John Brown, formerly of Edinburgh. See the 1 4th 

 Section of Dr. Darwin's Phytologia on this subject. 



