THE VITAL PRINCIPLE — THE BLOOD. 13 



seem to consist of little else than a quantity of 

 vital fluid. Of such are the large Medusa or 

 jelly fish, which we see floating on the surface 

 of the sea. They are composed of a most deli- 

 cate cellular tissue, rilled with fluid ; and this 

 being exhaled, as it often is, when individuals 

 are thrown upon the shore, and exposed to the 

 fervid rays of the sun, all that is left is a 

 slight filmy shred, a few grains only in weight. 



It is evident that the vital principle, in an 

 abstract sense, is beyond our research ; we can 

 only study it in its phenomena ; we can only 

 watch its effects and trace out its operations. 

 The Scripture, as we have seen, declares that 

 the " life of the flesh is in the blood." It will 

 be interesting, therefore, without entering very 

 abstrusely into the subject, to inquire as to the 

 composition of this fluid, at least in the higher 

 animals, and examine the mode in which its 

 losses are recruited, and its refreshment effected; 

 the more so, as in pursuing our inquiries it will 

 become manifest that both chemical and gal- 

 vanic changes or agencies are involved in the 

 phenomena connected with its waste and re- 

 newal. 



The blood of man or quadruped, when 

 poured out from the arteries or veins, is a red 

 viscid fluid, which, if suffered to remain for an 

 hour or two at rest in a vessel, separates, on 

 losing vitality, into two parts, one fluid, called 

 serum, the other tolerably solid, called clot or 

 crassamentum. Venous and arterial blood differ 

 from each other in colour, the former being of 



