CHAPTER VII. 



THE CAT'S ORGANS OF CIRCULATION. 



1. THE organs of circulation, or the circulating or vascular* 

 system, comprises all that great system of tubes (of very various 

 sizes) which have already been referred to, as arteries and veins, 

 and all the various channels, or vessels, by which the nutritive fluid 

 of the body the blood is conveyed to and from every part of the 

 cat's frame. 



That it should be so conveyed is a manifest necessity of life, for 

 since the process of nutrition takes place in the very innermost 

 substance of the body (as has been already pointed out), there must 

 be channels by which every part of the body may be supplied with 

 its needed nutriment. Such nutriment is to be found in the blood, 

 which has the power of repairing the waste of the tissues and sup- 

 plying the materials for assimilation and growth, but which cannot 

 obviously carry this power into effect except by moving from space 

 to space throughout the body without, that is, being propelled by 

 "organs of circulation," and without exuding from the ultimate 

 ramifications of such organs, to reach the very parenchyma itself. 



But we shall see in the next chapter that processes of gaseous 

 interchange, " respiration," and of the elimination of waste and other 

 products, " secretion," also really take place in the innermost paren- 

 chyma, and not on the surfaces of the inner lining of the tubes of 

 the various organs and internal cavities. Yet all that is so given 

 out or exchanged must (if respiration and secretion are to be effected) 

 find its way to such surfaces, and in order that it may be able so to 

 do, we also require the aid of the circulating system. But the blood, 

 in and by the very act of nourishing the various organs, must part 

 with its nutritive material, and this, therefore, requires to be re- 

 plenished if life is to be maintained. The needful gaseous matters 

 are obtained by it in respiration ; but the other matters have to be 

 gathered from materials prepared for it within the alimentary canal. 

 These materials, we have already seen, in part pass directly into the 

 blood-vessels which surround that canal, and in part into the vessels 



* A condition of vascularity (i.e., the I been attributed to certain tissues, such 

 presence of blood-vessels) has already I e.g. as the dermis, intestinal villi, &c. 



