tti AP. V. Other Relation* of ktoo<t. 



1. THE principal objects of blood are,' 1st, to furnish 

 the elements of the spirit ; and, 2nd, to furnish the elements of the 

 structures. The other relations, as Secretion, &c. being tributary 

 to these ends, are sfo far subordinate, and \vill be afterwards spoken of. 



2. The proof that life is maintained by that which is called 

 arterial blood is, that death quickly follows the interruption of the 

 process by which venous is converted into arterial blood. This 

 fact is sufficiently conclusive upon a question of the necessity of 

 arterial blood to the maintenance of life; but it is not altogether so 

 conclusive, as to the mode by which life becomes generally extinct 

 in consequence of suffocation. The alternatives are, 1st, that ar- 

 terial blood is required every where for the diffused assimilation of 

 the spirit; or, 2nd, that it is required by one organ, upon the 

 function or relations of which the diffused spirit is dependent. But 

 as the diffused spirit has been shewn to live by assimilation, so it is 

 impossible that such a principle should have any regular dependence 

 for assimilating properties, which, if originally derived from a dis- 

 tant source, are, by their capability to assimilate, rendered inde- 

 pendent of that source. Hence, as the second alternative appears to 

 be without foundation, or incompatible with other proofs, and no 

 other suggesting itself, we may venture to admit the first, vii. that 

 the assimilating life, which is the regular organic spirit of every part, 

 preserves itself by uniting its elements, which are informal, in 

 arterial blood. 



3. That the blood circulating in the arteries, although of the 

 kind proper for the purpose, is not that which maintains the life of 

 the artery, seems to be evinced by the fact, that a portion of an 

 artery, intercepted by ligature, through which blood ceases to flow, 

 preserves its life ; it contracts, and finally becomes almost ligamen- 

 tous; but if its life were extinct, its decomposition would ensue. 



4. If, then, the blood in those arteries which have been the 

 subjects of the observation does not maintain their life, it is next to 

 be inquired whether the blood in the smallest arteries is that from 

 which their spirit is renewed] If it were permitted to decide this 

 question by analogy, we should say, that as the texture of these ves- 

 sels is very similar, as the blood moves through them with con- 

 siderable velocity, and as no material difference is remarked between 



