162 INFECTIONS OF THE DIGESTIVE TRACT 



vaccinating with typhoid bacilli killed by heating to 

 60 to 65 C. a procedure which he dared to practice 

 after learning from Pfeiffer that he had in man obtained 

 the specific agglutination reaction of typhoid fever after 

 the subcutaneous inoculation of a heated culture of 

 typhoid bacilli. Chantemesse in 1904 obtained ap- 

 parently favorable results in the treatment of typhoid 

 fever by the use of a serum that developed in horses 

 treated with a filtrate from typhoid bacilli which had 

 grown on a medium containing splenic pulp and human 

 defibrinated blood. It is possible that this serum acts 

 by binding the "aggressins" made by the typhoid bacilli 

 as they grow, thus removing in some degree a condition 

 favorable for the multiplication of the typhoid bacilli. 



We may conveniently classify bacteria in a rough 

 way according to the degree of parasitism they exhibit. 

 Thus the plague bacillus in man and the anthrax bacillus 

 in guinea-pigs are highly parasitic, for they find in their 

 hosts the conditions that permit their rapid multiplica- 

 tion and invasion, although the original infection may 

 have been established by very few bacteria, perhaps even 

 by a single bacterium. Directly opposed to the parasites 

 stand the saprophytic bacteria, which have the utmost 

 difficulty in multiplying in the tissues of their host 

 even when introduced in large numbers, but may prove 

 injurious if inoculated in enormous quantities. Many 

 of the bacteria of the intestinal tract are of this character. 

 Midway between these groups stand the hemiparasites, 

 microorganisms which are invasive only when inoculated 

 in considerable numbers and are pathogenic only when 



