IMMUNITY AND SUSCEPTIBILITY 715 



ficially by the injection of bacteria, dead or alive, into the veins, sub- 

 cutaneous tissues or peritoneal cavity. In rare cases they may be pro- 

 duced by feeding the bacteria, injecting them into the air passages of 

 the lungs or by rubbing them into the skin. It is probable that the 

 highest concentration of agglutinins results from the injection of dead 

 bacteria. It is, however, necessary that these bacteria be not subjected 

 to a temperature above 62. Many pathogenic and non-pathogenic 

 bacteria form agglutinins when injected into the body. The concen- 

 tration of the agglutinins produced varies greatly. Very high agglu- 

 tinating sera are noted, such as, for example, one in one million when 

 B. typhosus is used and one in two million when Msp. comma of Asiatic 

 cholera is used. Often two strains of the same organism will vary 

 greatly in their power to produce agglutinins. Again, the concentra- 

 tion of the agglutinins in an infected animal varies from day to day, 

 and in order to make an accurate observation it is necessary to make 

 repeated examinations on subsequent days. For example, in typhoid 

 fever the agglutinins one day may be thirty times as strong as on a 

 subsequent day. 



The Distribution of Agglutinins in the Blood. As before stated, these 

 antibodies are found in practically all the body fluids. They reach 

 their highest concentration in all probability in the blood serum. In 

 certain cases they are in high concentration in the milk. Agglutinins 

 are also present at times in the sputum, tears, and the humors of the eye. 



Inherited Agglutinins. Agglutinating substances may be transferred 

 from the mother to the offspring in utero. It has been frequently 

 demonstrated, for example, that the offspring of mothers who have 

 recently recovered from typhoid fever or who are infected at the time 

 of the birth, have agglutinins in the body fluids. The same is true of 

 the offspring of glandered horses. Notwithstanding the fact that the 

 milk is frequently rich in agglutinins, these substances are not trans- 

 ferred to the offspring to any great extent by this means. 



The Substances Concerned in Agglutination. There are two distinct 

 substances concerned in this reaction, one substance which is present 

 in the serum or body fluids of the infected or immune individual, and 

 other substances which are present in the microorganisms which are 

 agglutinated. The substance in the serum, as before stated, is known 

 as the agglutinin; the substance (antigen) in the bacteria or other micro- 

 organisms is known as the agglutinogen. When agglutinins and agglu- 



