202 AGGLUTINATION 



serviceable in the identification of bacteria. A given bacterium is the 

 typhoid bacillus if it is agglutinated by the properly diluted serum of 

 an animal immunized to this organism. If an unknown culture is not 

 agglutinated by the serum of an animal immunized to the cholera 

 bacillus, the culture does not contain this organism. I have carefully 

 read the original paper of Gruber and Durham and fail to find therein 

 any reason for concluding that these investigators at that time had 

 any idea that the phenomenon which they were investigating was soon 

 to become one of the most certain and easily applicable methods for 

 the diagnosis of typhoid fever. It is true that they speak of the 

 serum test as a diagnostic measure, but from the context it is plainly 

 evident that by the term diagnosis they mean the specific and positive 

 identification of a suspected bacterium. A few months after the pub- 

 lication of this paper of Gruber and Durham, Widal demonstrated the 

 value of this reaction in the diagnosis of typhoid fever. 



Factors. It is evident that in such a reaction as that observed in 

 agglutination there must be two factors. One of these, designated the 

 agglutinin, is found in the serum, and the other, known as the agglutin- 

 able substance, exists in the bacterial culture. The product of the 

 reaction is known as the agglutinate. The serum of certain normal 

 animals has a slight agglutinating action on certain bacteria, notably 

 typhoid and colon bacilli. The normal serum of the horse, dog, 

 donkey, and rabbit, in an undiluted state, agglutinates typhoid cul- 

 tures. Some effect may be observed when the serum is diluted 1 : 30. 

 The serum of a man, who has never had typhoid fever, may agglutin- 

 ate typhoid cultures when the dilution is not higher than 1 :30. The 

 period in the progress of typhoid fever when marked agglutination 

 manifests itself varies widely. Usually it is not before the seventh 

 day, but it may occur as early as the second day, and it may be delayed 

 until the second week and in rare cases even later. Likewise the dis- 

 appearance of the reaction after recovery is variable. It may fail 

 within ten days after the loss of the fever, and it has been known to 

 continue for years. In intensity the reaction is variable and bears no 

 indication of the severity or seriousness of the disease. There are 

 many ways in which the phenomenon may be observed and measured. 

 One recommended by Widal and Sicard and much employed is the 

 following : 



