157 



paired by inflammation, so that they admit globules which they formerly 

 rejected. 



Some capillary vessels transmit blood at all times, and uniformly ex- 

 hibit a red colour : this is the case with the capillary vessels of the spleen, 

 of the corpora cavernosa of the penis, of the bulb and corpus spongiosum 

 of the urethra: the same applies to the capillaries of the muscles of the 

 mucous membranes : there arc, however, very few of those organs, in 

 v/hich the whole portion of the capillary tube, between the termination of 

 the artery and the origin of the vein, is filled with red blood. There is, 

 almost always, a division in the tortuous line described by the capillary, 

 and within this space, the blood cannot be detected of its usual colour*. 



The number of the capillary vessels, as well as that of the arteries, 

 to which the former are as auxiliaries, is much more considerable in the 

 secretory organs, than in those in \$hich life carries on only the process 

 of nutrition. It is on that account, that the Ijones, the tendons, the liga- 

 ments, the cartilages, contain so much smaller a quantity of blood, than 

 the mucous and serous membranes, and the skin. The capillary vessels 

 are, however, very numerous, in the muscles, which owe that colour to 

 the great quantity of blood they contain, but as we *hall point out, when 

 we come to speak of motion, this fluid appears to form an essential ele- 

 ment in muscular contraction; it is, therefore, not to be wondered, that 

 these organs should have a greater number of capillary vessels sent to 

 them: since these vessels do not supply them merely with molecules to 

 carry on nutrition, and to repair the waste of the part, but to impart to 

 them the principle of their frequent contraction ; the quantity of them is 

 so considerable, in all these parts, employed in the two-fold offices of nu- 

 trition and secretion, that Ruysch penetrated, with his injections, the 

 whole thickness of their substance, to such a degree, that the organs which 

 he had prepared, were only a wonderful and inextricable net-work of ca- 

 pillary vessels extremely minute. On these anatomical preparations, 

 made with an art hitherto unrivalled, Ruysch grounded his hypothesis 

 relative to the intimate structure of the body, in which, he imagined, all 

 was capillary tubes, an hypothesis which has obtained the most favoura- 

 ble reception, and has reigned, during more than a century in the schools. 

 It is enough to reflect a moment on their uses, to conceive that the num- 

 ber of them must be really prodigious. As long as the blood is enclosed 

 within the arteries, and flows under the contrcul of the heart, it fulfils no 

 purpose either of nutrition or secretion. To make it subservient to these 

 great functions, it must be diffused through the very tis:,u< of the organs, 

 by means of the capillary divisions; these little vessels exist then, in every 

 part, where any organized molecules are found united ; since the parti- 

 cle formed by their assemblage, must, at least, find, in the juices which 

 they bring to it, the materials of its reparation. Entering, in greater or 

 less proportion, into the organization of all the tissues, the capillaries re- 

 ceive certain modifications from the organs of which they are an integral 

 part; modifications which enable them to deposit the serous part of the 

 blood on the surface of the serous membranes, admit the transudation of 



* There is every reason for concluding that capillary vessels exist, which, running- 

 between some of the terminations of the arteries and the commencement of veins, ad- 

 mit only the serous portion of the blood, when performing- their healthy functions ; but 

 which may, in a state of inflammation, admit also the red particles of this fluid to flow 

 along them. Copland 



