248 PATHOLOGY OF THE BLOOD AND CIRCULATION. 



flammation. He froze the ear of a rabbit and then allowed it 

 to thaw, thus exciting considerable inflammation. The animal 

 was killed when the process was at its height, the bloodves- 

 sels of the head injected, and the ears removed and dried. 

 The unin flamed ear was clear and transparent, and the blood- 

 vessels easily seen ; the inflamed ear was thick and opaque, 

 and the arteries much enlarged. 



A few years later very numerous indeed are the papers and 

 monographs describing the changes in the size of the blood- 

 vessels in an inflamed animal membrane studied under the 

 microscope. A frog was restrained in a muslin bag and to 

 the web of the foot less frequently to its mesentery or to 

 the web of the foot of a young duck similarly restrained 

 various irritants were applied and the results noted under the 

 microscope. The increased size in the capillary bloodvessels 

 was thus observed in the affected area, and further a marked 

 slowing in the rapidity of the blood-current. 



By 184-0 we find the description much more complete. 

 Addison and others carefully described, in addition, an axial 

 stream of red blood-cells and a much more slowly moving 

 peripheral stream in which were found the leukocytes ; and 

 as the velocity of the circulation became less and less the 

 great accumulation of the latter along the inner wall of the 

 vessels was noted. Addison maintained the identity of the 

 leukocyte and pus-cell ; and even the passage of the leukocytes 

 through the bloodvessel-walls was described, but failed to at- 

 tract much attention ; a phenomenon which, since the work 

 of Cohnheirn, twenty-eight years later, has been studied with 

 great interest. 



The experiments of Cohnheim (1867), though they simply 

 duplicated the experimental studies of earlier observers on 

 living animal membranes, were of the greatest importance, for 

 to him undoubtedly all credit is due for our knowledge of the 

 migration of the leukocytes, the announcement of which came 

 as a surprise to all. 



Microscopical appearances of inflamed animal membranes : 

 First stage: Dilatation of vessels; acceleration of blood-current. 

 When the mesentery of a curarized frog is exposed under the 

 microscope there is soon noted a dilatation of the arteries and 

 then of the veins, and to a very much less degree of the capil- 



