118 ELEMENTS OF APPLIED MICROSCOPY. 
closely resembling the diphtheria organism, may be 
present. 
7. The Serum Reaction in Typhoid Fever.—One of 
the most important practical results of the rscent 
marvellous progress in the study of the phenomena 
of immunity has been a method for the clinical diag- 
nosis of typhoid fever and certain other diseases. It 
YX 
Fic. 46.—DIPHTHERIA Bacittt (METHYLENE BLur). (After Wes- 
brook.) Diagrammatic. 
has been shown that when the animal body is invaded 
by a parasitic micro-organism, the cells produce in some 
cases antitoxins which neutralize the poisons of the 
microbe, and in other cases anti-bodies of another type 
which have a specific destructive action on the parasite 
itself. Sometimes the defensive secretions dissolve the 
