386 TYPHOID FEVER 



with which diseases caused by allied organisms are concerned, 

 as it is probable that all the forms which these take in man 

 have not been recognised. The very wide application of the 

 reaction has elicited the fact that it is given in many cases of 

 slight, transient, and ill-defined febriculae, which occur especially 

 when typhoid fever is prevalent. Some of these may be aborted 

 typhoid, some may be paratyphoid. There is no doubt that, if 

 all the facts are taken into account, the cases where the reaction 

 gives undoubtedly correct information so far outnumber those in 

 which an error may be made that it must be looked on as a 

 most valuable aid to diagnosis. In conclusion, here we may say 

 that the fact of a typhoid serum clumping allied bacilli in no 

 way, so far as our present knowledge goes, justifies doubt being 

 cast on the specific relation of the typhoid bacillus to typhoid 

 fever. 



In connection with the phenomenon that a serum either from 

 a normal person or a typhoid patient may clump several varieties 

 of bacteria, some points arise. The theoretical consideration of 

 agglutination is reserved for the chapter on Immunity, but here 

 it may be said that agglutinating properties may be present 

 normally in a serum or they may be originated by an animal 

 being infected with a particular bacterium. As the result of 

 injecting a bacterium, not only may agglutinins capable of acting 

 on that bacterium appear in the serum, but the serum may 

 become capable of agglutinating other, and especially kindred, 

 bacteria; further, any normal agglutinins for the infecting 

 bacterium present in the serum may be increased in amount. 

 The agglutinin acting on the infecting organism has been called 

 the primary or homologous agglutinin, while the others have 

 been called the secondary or heterologous agglutinins. But 

 besides what we know to be a fact, that infection by a single 

 bacillary species can originate agglutinins acting both on itself 

 and on allied species, we must consider the possibility of 

 infections by more than one species occurring in an animal, e.g., 

 b. typhosus with b. coli or with b. paratyphosus (vide infra). In 

 such a case each organism may originate its primary agglutinin, 

 so that the presence of multiple agglutinins in a serum may 

 really be an indication of a mixed infection. Some attention 

 has been directed to the diagnosis and differentiation of these 

 conditions. Castellani introduced the absorption method for 

 their investigation (for method, see p. 122), and by this means 

 studied the primary and secondary agglutinins produced in 

 infections in rabbits ; he found that when an animal had been 

 infected with b. typhosus this organism would absorb from its 



