CA USES OF DISEASE. 2 2 1 



has been known since the time of Celsus that the 

 cardinal signs of inflammation in a warm-blooded 

 animal are redness, swelling, heat, and pain. The red- 

 ness is due to afflux of blood, the swelling to an increased 

 quantity of fluid in the part, the excess of heat is con- 

 sequent on the extra tissue-change, and the pain to 

 pressure on the nerves of the inflamed part. The in- 

 genuity of pathologists has devised plans whereby the 

 inflammatory process can be actually watched in such 

 situations as the web of the frog's foot, in the tongue of 

 the frog, and in the mesentery of the mouse. One of the 

 most striking events seen on irritating the parts either 

 by acid, by foreign bodies, or the introduction of bacteria, 

 is the emigration of leucocytes from the walls of the 

 vessels. How the leucocytes escape from the capil- 

 laries is a mystery, but that they make their way through 

 the vessel-wall is one of the best ascertained facts of 

 experimental pathology. 



The emigrated leucocytes then proceed to attack the 

 intruding matter, and usually effect its removal, but failing 

 this may encyst it in the way already explained. When 

 the invaders are bacilli they may overrun the organism 

 by gaining entrance into the circulatory system. The 

 experimental evidence, and our better knowledge of 

 intra-cellular digestion, shows clearly that, zoologically 

 considered, inflammation is in essence a local struggle 

 between irritants and the white cells of the blood. When 

 the whole of the blood is engaged in the struggle, as in 

 ague, pyaemia, anthrax, and the like, we have general 

 inflammation or fever. The different varieties of fever, 

 when due to micro-organisms, depend on the habits 



