294: CIRCULATION. 



necessary to discuss the views of Bichat, and some others, 

 who supposed that the action of the heart had no effect upon 

 the capillary circulation. It must be admitted that this is its 

 prime cause ; and the only questions to be considered are, 

 first, whether there be any reason why the force of the heart 

 should not operate on the blood in the capillaries, and 

 second, whether there be any force in these vessels which 

 is superadded to the action of the heart. 



The first of these questions is answered by microscopic 

 observations on the circulation. A distinct impulse, follow- 

 ing each ventricular systole, is observed in the smallest ar- 

 teries. The blood flows from them directly and freely into 

 the capillaries ; and there is not the slightest ground for the 

 supposition that the force is not propagated to this system of 

 vessels. 



Yarious writers have supposed the existence of a " capil- 

 lary power," which they have regarded as of greater or less 

 importance in producing the capillary circulation. The 

 views of some are purely theoretical, but others base their 

 opinion on microscopic observations. These views do not 

 demand an extended discussion. There is a force in opera- 

 tion, the action of the heart, which is capable of producing 

 the capillary circulation ; and there is nothing in the phenom- 

 ena of the circulation in these vessels, which is inconsistent 

 with its full operation. Under these circumstances, it is 

 unphilosophical to invoke the aid of the currents produced 

 in capillary tubes in which liquids of different characters a,re 

 brought in contact, or a " capillary power " dependent upon 

 a vital nutritive attraction between the tissues and the blood, 

 unless we do it on the basis of phenomena observed in the 

 capillaries when the action of the heart is suppressed. 

 When the heart ceases its action, movements in the 

 capillaries are sometimes due to the contractions of the ar- 

 teries, a property which has already been fully considered. 

 Movements which have been observed in membranes de- 

 tached from the body are due to the mere emptying of the 



