522 THE THIRD HUXLEY LECTURE 



corpuscles, both red and white, moved along with the plasma with the most 

 perfect freedom. 



But I was not altogether satisfied with this evidence of their entire absence 

 of adhesiveness within healthy vessels, because the aggregation of the red discs 

 in the frog is of a somewhat indefinite character. I therefore sought further 

 light upon the point in the mammalian bat. Having placed one under chloro- 

 form and extended one of its wings under the microscope, I temporarily arrested 

 the circulation by compressing the main vessels of the limb ; and on examining 

 one of the veins I was much disappointed to see the red corpuscles of its con- 

 tained blood aggregated. It seemed possible, however, that the part of the 

 membrane which I was examining might be suffering mechanical irritation 

 from pressure between the glass slide on which it rested and the cover-glass 

 which it was necessary to use with the high magnifying power required for the 

 bat's wing. For those were not the days of immersion lenses. I therefore 

 made arrangements to guard against the possibility of such an occurrence ; 

 and now, to my great joy, I beheld the red corpuscles, which lay motionless 

 in a considerable venous channel, distributed uniformly through the plasma, 

 without the slightest appearance of aggregation. 



The animal having been killed immediately afterwards, I examined a drop 

 of blood from its heart. The contrast with what I had seen in the healthy 

 living vessel was most striking ; the red corpuscles presenting a degree of 

 adhesiveness such as I had never before seen equalled, whether outside the 

 body or within the vessels. When forced to separate from each other by 

 pressure made upon the cover-glass, they became drawn out like threads of 

 a viscid liquid before becoming completely detached. The animal had been 

 suffering from a bad compound fracture in one of the wings. Whether the 

 great adhesiveness of the red discs of the shed blood was due to inflammation 

 caused by the injury, or whether such a condition is normal to the bat, as it 

 is to the horse and the ass, I do not know. 



By such facts it seemed to be established that the stasis of the blood in 

 an irritated area, that is to say, the accumulation of the blood-corpuscles, both 

 red and white, in the vessels of that area, is due to a tendency on their part to 

 adhere to each other and to the walls of the vessels ; that they do this by virtue 

 of an adhesiveness or viscidity which they do not manifest at all within the 

 vessels of a perfectly healthy part, and which, while varying in degree with the 

 severity of the irritation, never seems to exceed that which is observed in blood 

 outside the body.^ 



What was it that induced the blood corpuscles to assume this adhesiveness 



^ Vide Phil. Trans., 1858 (see vol. i, p. 217). 



