65 



The function of the capillaries is to distribute the nutritive 

 elements to the most minute portions of the tissues. 



The arteries themselves are not supplied with nutriment from 

 the biood that passes through them, but by vessels from the col- 

 lateral branches termed the vasa vasorum. These minute sys- 

 tems within systems remind one of the Hudibrastic conceit : 



" Great fleas have little fleas 



Upon their backs, to bite 'em, 

 And little fleas have lesser fleas ; 

 And so, ad infinitum" 



A certain regulative or distributive power exists in the walls 

 of the capillaries, on the tissues which they traverse. 



PHYSIOLOGICAL FACTS. 



Though the red cells of the blood pass through them, as a 

 rule, in single file, sometimes the capillaries enlarge to admit 

 several files to pass at once. The velocity of the current is 

 liable to great and sudden variations from local influences, and 

 when the action of the heart is enfeebled, stagnation some- 

 times takes place, which is often overcome by the vigorous ac- 

 tion of the heart. 



Impairment of the functions of the blood, by which it is not 

 duly aerated, retards the flow of the blood through the capil- 

 laries, the tissues being deprived of the proper amount of their 

 appropriate stimulus. This has been verified by experiment 

 in the lungs. The change in the condition of the blood in re- 

 gard to the relative proportions of its oxygen and carbonic acid 

 is the only one to which the pulmonary circulation is subservi- 

 ent. 



Any circumstance which increases the functional energy of 

 a part, or stimulates it to increased nutrition, will occasion an 

 increase in the supply of blood, irrespective of any change 

 in the heart's action. An undue acceleration of the local cir- 

 culation constitutes the state known as active congestion, hy- 

 peremia, or determination of blood. 



