THE CIRCULATION. 



44. Assimilation. The crowning act of the circula- 

 tion, the furnishing of supplies to the different parts of 

 the body, is effected by means of the capillaries. The or- 

 gans have been wasted by use ; the blood has been enriched, 

 by the products of digestion. Here, within the meshes of 

 the capillary network, the needy tissues and the needed 

 nutriment are brought together. By some mysterious 

 chemistry, each tissue selects and withdraws from the 

 blood the materials it requires, and converts them into a 

 substance like itself. This conversion of lifeless food into 

 living tissue is called assimilation. The process probably 

 takes place at all times, but the period especially favorable 

 for it is during sleep. Then the circulation is slower, and 

 more regular, and most of the functions are at rest. The 

 body is then like some trusty ship, which after a long voy- 

 age is "hauled up for repairs." 



45. Iiyuries to the Blood-vessels. It is important 

 to be able to discriminate between an artery and a vein, in 

 the case of a wound, and if we remember the physiology 

 of the circulation we may readily do so. For, as we have 

 already seen, haemorrhage from an artery is much more 

 dangerous than that from a vein. The latter tends to cease 

 spontaneously after a short time. The arterial blood flows 

 away from the heart with considerable force, in jets; its 

 color being bright scarlet. The venous blood flows toward 

 the heart from that side of the wound furthest from the 

 heart; its stream being continuous and sluggish; its color 

 dark. In an injury to an artery, pressure should be made 

 between the heart and the wound ; and in the case of a 

 vein that persistently bleeds, it should be made upon the 

 vessel beyond its point of injury. 



44. What is meant by assimilation ? What can you say of its use, etc. ? Time ? 



45. What is stated of the injuries to the blood-vessels ? 



