AND ANIMAL LIFE. 179 



is natural, it is less perfectly arterialized ; and 

 whenever the contrary state is present, its qua- 

 lities are improved. 



CXCVIII. CRAWFORD remarks, that, when an 

 animal has been exposed for some time to a high 

 temperature, the blood in the veins assumes the 

 colour of that which circulates in the arteries. He 

 explains this appearance, by stating, that " the 

 sanguineous fluid is less impregnated with the 

 inflammable principle," or, to employ terms more 

 intelligible to modern readers, that the blood has 

 not undergone its accustomed changes in the ca- 

 pillaries of the body, and therefore is less penalized. 

 When the system is subjected to great heat, less 

 blood at any one moment is transmitted through 

 the lungs, the consequence of which is, that it is 

 more perfectly arterialized, and, from the increas- 

 ed action of the heart, returns to the chest in 

 about one half of the usual time. It is therefore 

 manifest, that the blood is favourably circum^ 

 stanced for the operation of chemical changes ; 

 on the one hand its quantity is diminished, and on 

 the other the repetition of these changes is doub- 

 led. These reasons alone are sufficient to explain 

 the altered colour of the blood. 



CXCIX. As CRAWFORD had found this ap- 

 pearance in every instance in which an animal 

 was submitted to warm air or water, he was de- 

 sirous of trying the effects of cold air or water. 

 For this purpose, a dog was immersed in water 

 M 2 



