570 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



of the bacteria, but they will not produce a clumping or agglutinate. 

 Occasionally in some fresh sera, substances are found which have a 

 greater affinity for the agglutinogen of the bacteria than the agglutinins 

 have. Such substances are designated as proagglutinoids and are in 

 this respect similar to protoxoids. 



The Stages of Agglutination. There are two distinct stages of the 

 agglutination reaction. Neither of these stages can take place unless 

 some salts or electrolytes are present. Sodium chloride is the common 

 salt present. The first phase of the agglutination reaction is a union 

 between the agglutinin and the agglutinogen of the bacteria. The 

 second phase is the actual clumping of the bacteria. It is supposed that 

 in this last phase the zymogenic group of the agglutinin is acting. In 

 the first phase the haptophile group of the agglutinin is combined with 

 the haptophore group of the agglutinogen. 



There are some bacteria that cannot be agglutinated, as for example, 

 Bad. pneumonia of Friedlander, and in rare instances B. typhosus 

 cannot be agglutinated. It is possible, for example, to grow B. typhosus 

 at a temperature of 42 and cause it to lose its power of producing agglu- 

 tinins. Bacteria may also be modified chemically so that they will lose 

 the power to produce agglutinins. 



Agglutinins bear no relationship to bactericidal substances, antitox- 

 ins, opsonins, or any of the other antibodies. They are of use in 

 the determination of species of bacteria when a known agglutinating 

 serum is at hand, and they are also of use in determining the cause of 

 infections where a known culture or agglutinogenic substance is at hand. 

 The agglutination reaction is used in the diagnosis of typhoid fever, 

 paratyphoid fever, glanders, and dysentery. 



Hemoagglutinins. Agglutinating substances are sometimes pro- 

 duced for red blood corpuscles when these bodies are used in the 

 immunization of an animal. Such agglutinins when combined with the 

 corpuscles produces a clumping which is known as hemoagglutination. 

 The mechanism of the reaction is the same as that of bacterial agglutinins. 

 It is possible that hemoagglutination is one important factor in the pro- 

 duction of agglutination thrombi in certain infectious diseases. 



PRECIPITINS. Another group of substances, which are antibodies, 

 are produced through the processes of immunization which have not been 

 definitely connected with the phenomena of immunity. These substances 

 are known as the precipitins. Precipitins may be produced for the protein 



