OE THE CAPILLARY VESSELS. 2G1 



almost impossible to solve these questions. Were they not 

 rather accidental passages? 



Those who have since admitted the existence of serous ves- 

 sels, appear to have been ignorant of this, being the most pow- 

 erful fact in favour of their opinion. Those who have rejected 

 them, have also passed it over in silence. 



The opinion of Mascagni, Prochaska, and others, respect- 

 ing the non-existence of vessels finer than those which give 

 passage to a single coloured globule of blood, may be esta- 

 blished, first, upon the circumstance, that these vessels are 

 easily seen by the aid of the microscope in living animals, and 

 by no means smaller vessels, although the microscope gives so 

 large a volume to the globules of the blood, that it would be 

 easy to distinguish much smaller objects; secondly, upon the 

 circumstance that the red injection, which is very penetrating, 

 does not clearly disclose any other vessels than those which 

 are seen in the living subject. If in this case the parts become 

 more red, especially after desiccation, it may be owing to the 

 dilatation of the vessels, and to the disappearance of the inter- 

 mediate substance. If inflammation reddens the parts still 

 more, it is by the dilitation of the existing vessels, the forma- 

 tion of new ones, and the infiltration of blood between the ves- 

 sels. As to the whiteness or natural want of colour of certain 

 very vascular parts, as the conjunctiva, it depends upon the 

 circumstance, that the capillary vessels being in these parts ex- 

 tremely small, the colour of the blood can not be perceived in 

 them. 



3S8. The question, therefore, which relates to the exist- 

 ence of the colourless capillary or serous vessels, is very diffi- 

 cult or impossible to answer; and when this expression is used 

 in the present work, it is to designate capillary vessels which, 

 whether they contain only the serum of the blood, or the blood 

 in its entire state, but in series of single globules, which pre- 

 vents its colour from being perceived, are colourless in the or- 

 dinary state. It is more consistent however with reason not 

 to admit the existence of vessels which no one has ever seen. 

 389. In the double circle of the circulation, the evident 

 communication of the arterial and venous trunks occur in the 



