376 THE LAWS OF ORGANIC 



perties were present. I shall attempt, in the fol- 

 lowing pages, to show in what way the quality 

 of the blood is improved, and also what is the 

 agent ; w r e shall then be still better able to judge 

 of the principle of life. These observations 

 suggest to the surgical operator the necessity of 

 preserving, as much as possible, the vital fluid 

 for the benefit of the system, when such is im- 

 peratively demanded. This object is accom- 

 plished by applying the tourniquet, or similar 

 means, to the trunks of the principal arteries 

 belonging to the limb, for a few minutes previ- 

 ous to the operation. When the extremity is 

 thus circumstanced, the arterial blood is neces- 

 sarily very much impeded in its flow to the 

 limb, if not almost suppressed, while, at the same 

 time, the venous does not experience an equal 

 difficulty in its return. 



CCCCXLIX. The observations and precepts of 

 mankind, in general, are frequently more valu- 

 able than the man of science is disposed to allow. 

 The basis of the greater part of our knowledge 

 has been formed by contributions derived from 

 vulgar opinion and experience ; and, even at the 

 present moment, the medical practitioner is, to 

 a very great extent, directed in the treatment of 

 diseases, by rules, if not entirely empirical, par- 

 taking considerably of this character. In illus- 

 tration of these sentiments, it is generally stated 



