CHAPTEK VII. 



CIRCULATION OF THE BLOOD IN THE CAPILLARIES. 



Distinction between capillaries and the smallest arteries and veins Physiological 

 anatomy of the capillaries Peculiarities of distribution Capacity of the 

 capillary system Course of blood in the capillaries Phenomena of the 

 capillary circulation Rapidity of the capillary circulation Relations of the 

 capillary circulation to respiration Causes of the capillary circulation In- 

 fluence of temperature on the capillary circulation Influence of direct irrita- 

 tion on the capillary circulation. 



BEFORE entering upon the study of the capillary circu- 

 lation, let us define what we mean by the capillary vessels, 

 as distinguished from the smallest arteries and veins. From 

 a strictly physiological point of view, the capillaries should 

 be regarded as commencing at the point where the blood is 

 brought near enough to the tissues, to enable them to sep- 

 arate the elements necessary for their regeneration, and give 

 up the products of their physiological decay. With our 

 present knowledge, it is impossible to assign any limit where 

 the vessels cease to be simple carriers of blood ; and it does 

 not seem probable that it will ever be known to what part of 

 the vascular system the processes of nutrition are exclusively 

 confined. The divisions of the blood-vessels must be, to a 

 certain extent, arbitrarily defined, and we should feel at lib- 

 erty to adopt the views of any reliable observer with regard 

 to the kind of vessels which are to be considered as capilla- 

 ries. The most simple, and what seems to be the most phys- 



