CAUSES OF DISEASE. 221 
thas 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, pyzmia, anthrax, and the like, we have general 
inflammation or fever. The different varieties of fever, 
when due to micro-organisms, depend on the habits 
