ASSIMILATION OF BLOOD. 105 



virus ; in other words, the blood exactly assimilates to its 

 altered self the materials derived from the lymph and chyle. 

 In health we cannot see the precision of the adjustment 

 of the blood to the tissues ; but we may imagine it from 

 the small influences by which, as in vaccination, it is 

 disturbed ; and we may be sure that the new blood is as 

 perfectly assimilated to the healthy standard as in disease 

 it is assimilated to the most minutely altered standard.* 



How far the assimilation of the blood is effected by any 

 formative power which it may possess in common with the 

 solid tissues, we know not. That this possible formative 

 power is, however, if present, greatly ministered to and 

 assisted by the actions of other parts there can be no doubt ; 

 as, ist, by the digestive and absorbent systems, and pro- 

 bably by the liver, and all of the so-called vascular glands ; 

 and, zndlt/, by the excretory organs, which separate from 

 the blood refuse materials, including in this term not only 

 the waste substance of the tissues, but also such matters 

 as, having been taken with food and drink, may have been 

 absorbed from the digestive canal, and have been sub- 

 sequently found unfit to remain in the circulating current. 

 And, yrdly, the precise constitution of the blood is adjusted 

 by the balance of the nutritive processes for maintaining 

 the several tissues, so that none of the materials appro- 

 priate for the maintenance of any part may remain in 

 excess in the blood. Each part, by taking from the blood 

 the materials it requires for its maintenance, is, as has 

 been observed, in the relation of an excretory organ to all 

 the rest ; inasmuch as by abstracting the matters proper 

 for its nutrition, it prevents excess of such matters as 

 effectually as if they were separated from the blood and 

 cast out altogether by the excreting organs specially present 

 for such a purpose. 



* Corresponding facts in relation to the maintenance of the tissues by 

 assimilation will be mentioned in the chapter on NUTRITION. 



