1 64 THE CIRCULATIOX. 



could not escape from the circulating stream, unless the 

 wall of the containing blood-vessel were ruptured. It is 

 true that an English physiologist, Dr. Augustus Waller, 

 affirmed in 1846, that he had seen blood- corpuscles, both 

 red and white, pass bodily through the wall of the capillary 

 vessel in which they were contained; and that, as no opening 

 could be seen before their escape, so none could be observed 

 afterwards so rapidly was the part healed. But these ob- 

 servations did not attract much notice until the phenomena 

 of escape of the blood-corpuscles from the capillaries and 

 minute veins, apart from mechanical injury, was redis- 

 covered by Professor Cohnheim in 1867. 



Professor Cohnheim' s experiment demonstrating the pass- 

 age of the corpuscles through the wall of the blood-vessel, 

 is performed in the following manner. A frog is curarized, 

 that is to say, paralysis is produced by injecting under the 

 skin a minute quantity of the poison called curare ; and 

 the abdomen having been opened, a portion of small in- 

 testine is drawn out, and its transparent mesentery spread 

 out under a microscope. After a variable time, occupied 

 by dilatation, following contraction, of the minute vessels, 

 and accompanying quickening of the blood-stream, there 

 ensues a retardation of the current ; and blood-corpuscles, 

 both red and white, begin to make their way through the 

 capillaries and small veins. The process of extrusion of 

 the white corpuscles is thus described by Dr. Burdon San- 

 derson, and the passage of the red corpuscles occurs after 

 much the same fashion. 



" Simultaneously with the retardation, the leucocytes, 

 instead of loitering here and there at the edge of the axial 

 current, begin to crowd in numbers against the vascular wall, 

 as was long ago described by Dr. Williams. In this way 

 the vein becomes lined with a continuous pavement of these 

 bodies, which remain almost motionless, notwithstanding 

 that the axial current sweeps by them as continuously as 

 before, though with abated velocity. Now is the moment 



