500 



is, that the pus corpuscles are not only similar in form to the white 

 blood cells, but that they actually are blood cells which have, aided by 

 certain conditions of the circulation in inflamed parts, passed through 

 the uninjured walls of the blood vessels and become free. 



The following is a short sketch of the observations on which this 

 theory is based. When the cornea was made to inflame, the suppuration 

 was found always to begin at the edge, and to travel towards the centre, 

 and this whether the irritant was applied to the central parts or to the 

 periphery. Now, the cornea is a tissue which contains no blood vessels 

 of its own, but whose borders join on to vascular parts. Furthermore, 

 at all stages of the suppurative process the cornea cells could be seen 

 unaltered in the midst of the pus cells, and the former never showed 

 any sign of proliferation, or of undergoing change into the latter. 



Lastly, when coloured substances in a minute state of division were 

 injected into the blood, they were taken up by the white blood cells, 

 which were by this means marked, and could be traced in their wander- 

 ings through the body. If, in an animal thus treated, a keratitis was 

 excited, among the pus cells found in the cornea were always a number 

 which contained coloured particles, showing that some, at all events, of 

 the pus cells had been at a former time blood corpuscles. 



At this point it became necessary to observe the process of inflamma- 

 tion in some vascular part where the passage of the blood cells through 

 the walls of the vessels might be seen, if such a process did really occur. 

 As the subject of his observations for this purpose Cohnheim chose the 

 mesentery, or transparent membrane which binds the intestine to the 

 back wall of the abdomen, and in which the vessels going to and return- 

 ing from the intestine are found. The animals used were frogs. A 

 few experiments made also on young rabbits and kittens, although 

 attended with much difliculty, and much more imperfect in their results 

 than those performed on frogs, showed, nevertheless, that the pheno- 

 mena of the inflammatory process were essentially the same in warm as 

 in cold blooded animals. The method of preparation adopted in the 

 case of the frog is as follows. The animal is first poisoned with a 

 small dose of curara, which prevents all voluntary movement, paralysing 

 the peripheral extremities of the motor nerves, while the circulation 

 goes on unimpaired. "When the frog becomes motionless, a small open- 

 ing is made through the side into the abdomen, and through this the 

 intestine is drawn out. The animal is then laid on his back on a large 

 glass plate, on which a small disc of glass, surrounded by a narrow ring 

 of cork, has been cemented with Canada balsam. Over this disc the 

 mesentery is laid ; and the intestine which comes to lie on the cork ring 

 is attached to this by a few small pins, so as to prevent displacement of 

 the object by the peristaltic movements of the intestinal muscular fibres. 

 The mesentery may or may not be covered with a piece of thin glass — 

 Cohnheim prefers to examine it uncovered ; and I have found it best to 

 do so, for the sharp edge of the covering glass is very apt to injure 

 some of the small blood vessels of the delicate mesenteric tissue, and to 

 cause haemorrhage, which completely destroys the object. When thus 



