138 T H E ( ; I R C U L A T I O N. 



Part of this slow movement of the pale corpuscles and their 

 occasional stoppage may be due, as E. H. Weber has suggested, 

 to their having a natural tendency to adhere to the walls of 

 the vessels. Sometimes, indeed, when the motion of the blood 

 is not strong, many of the white corpuscles collect in a capil- 

 lary vessel, and for a time entirely prevent the passage of the 

 red corpuscles. But there is no doubt that such a still layer 

 of liquor sanguinis exists next the walls of the vessels, and it 

 is between this and the tissues around the vessels that those 

 interchanges of particles take place which ensue in nutrition, 

 secretion, and absorption by the bloodvessels; interchanges 

 which are probably facilitated by the tranquillity of the fluids 

 between which they are effected. 



Until within the last few years it has been generally sup- 

 posed that the occurrence of any transudation from the inte- 

 rior of the capillaries into the midst of the surrounding tissues 

 was confined, in the absence of injury, strictly to the fluid part 

 of the blood ; in other words, that the corpuscles could not es- 

 cape from the circulating stream, unless the wall of the con- 

 taining bloodvessel 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 observations 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 rediscovered by Professor Cohnheim in 1867. 



Professor Cohnheim's experiment demonstrating the passage 

 of the corpuscles through the wall of the bloodvessel, is per- 

 formed 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 intestine is drawn out, 

 and its transparent mesentery spread out under a microscope. 

 After a variable time, occupied by dilatation, following con- 

 traction, 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 Sanderson, and the passage of the red corpuscles oc- 

 curs after much the same fashion. 



"Simultaneously with the retardation, the leucocytes, in- 

 stead of loitering here and there at the edge of the axial cur- 



