OF THE AETEEIES. 291 



organization of the capillaries of the villi, which is 

 constantly observed in this disease, follows.* In 

 every part of the body the bioplasts of the capillary 

 vessels, as well as white blood corpuscles, and lymph 

 corpuscles, are agents which take up excrementitious 

 matter and products of decay, and pass these on in 

 an altered form into the blood where they undergo 

 farther change, being probably split up into matters 

 which are appropriated as pabulum, and noxious 

 substances which are very soon excreted from the 

 body. 



299. Of the arteries. — The walls of the larger 

 arteries consist chiefly of elastic tissue but in the 

 intervals between the fibres of this structure, or in 

 the meshes of the elastic network, are seen in some 

 cases many elongated and triangular elementary 

 parts of involuntary muscular fibre. The so-called 

 muscular fibre cells were first demonstrated by 

 KoUiker. I have given figures of them. It is to the 

 presence of these bodies that the contractility of the 

 larger vessels is entii-ely due. That these vessels 

 are capable of contraction was proved experimentally 

 by John Hunter, but the degree of contractile power 

 is comparatively shght, and as far as they are con- 

 cerned in the physics of the circulation the large 

 arterial ramifications may be considered simply as 

 elastic tubes. 



In the smaller and smallest arteries, however, the 

 case is very different indeed. To such a degree are 

 the walls of these tubes capable of being contracted, 

 that the cavity of the vessel may be temporarily 

 obliterated. The little arteries of every part of the 

 body undergo great changes in their calibre. Pro- 

 bably many times during the twenty-four hours 

 the blood carrent is reduced and augmented, the 

 vessel changing to an extent equal to two or three 



* " Disease Germs : their Natvire and Origin ; and on the 

 Treatment of the Feverish State." 2nd edition. 



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