AGGLUTINATION AND PRECIPITATION 151 



therefore, are likewise of different types. It is entirely probable 

 that closely related organisms should throw off some identical 

 agglutinogen, and, therefore, have some common agglutinins. 

 Agglutination of an organism by a heterologous serum is termed 

 group agglutination. The agglutinins which are specific for the 

 organism are called its chief agglutinins, and those common to two 

 or more organisms are termed coagglutinins. It may sometimes 

 be shown that differences exist between the agglutinins produced 

 by different strains of the same organism. The importance is 

 apparent, therefore, of using care in testing the agglutinating power 

 of any serum to dilute to such an extent that the action of the 

 coagglutinins may be negligible and that of the specific or chief 

 agglutinins, recognized. 



Agglutination Tests in Disease Diagnosis. The fact that an 

 organism developing in the body generally excites the production 

 of a specific agglutinin has led to the wide use of the fact in the 

 diagnosis of certain infectious diseases. Not all diseases cause 

 an appreciable production of agglutinin. The test is carried out 

 by mixing serum from the suspect with the organism. If agglu- 

 tination occurs in proper dilution, it is evident that the specific 

 organism is or has been present in the patient. The test is fre- 

 quently reversed, and serum from an animal showing high agglu- 

 tinating power is used to differentiate between different species 

 and races of bacteria. The principal disease organisms which cause 

 the production of appreciable amounts of agglutinin are as follows : 

 Bacillus typhosus (typhoid fever), Bacillus paratyphus (paraty- 

 phoid) , Bacillus enteritidis (meat-poisoning) , Bacillus dysenteric (ba- 

 cillary dysentery), Bacillus coli, Bacillus pyocyaneus, Bacillus mallei 

 (glanders), Bacillus pestis (bubonic plague), Bacillus tuberculosis 

 (tuberculosis), Micrococcus melitensis (Malta fever), Streptococcus 

 pyogenes, and some other pyogenic cocci, Micrococcus meningitidis 

 (epidemic cerebrospinal meningitis), Spirillum cholera? (Asiatic 

 cholera), and others. The test is not commonly used in practice 

 for the recognition of all of them some are of experimental interest 

 only. 



The diagnosis of disease by agglutination is commonly called 

 the " Gruber-Widal," or simply the " Widal " test. The test may 

 be made either by. observation of a hanging drop or microscopically, 



