REACTION OF THE HOST TO INFECTION 211 



cipitinogen, and is specific in nature, and another which brings 

 about the change evidenced by formation of the precipitate^ 

 The former of these chemical groups is called the combining or 

 haptophorous group or haptophore, and the latter is called the 

 ferment-bearing or zymophorous group or zymophore. This 

 type of side-chain is Ehrlich's receptor of the second order. It 

 is represented in the figure as possessing one smooth branch 

 which serves for simple attachment, the haptophore, and one 

 branch equipped with saw-teeth to suggest its property of pro- 

 ducing chemical change, the zymophore. The precipitin pres- 

 ent in the blood plasma is supposed to consist of such receptors 

 which have become detached from the cell producing them. 



Agglutinins. Gruber and Durham (1896) found that the 

 blood of animals suffering from certain infections has the power 

 of causing the bacteria involved to clump together and lose their 

 motility when it is added to a broth culture or a suspension of the 

 bacteria in salt solution. The phenomenon has been observed 

 in connection with many bacteria, not only motile but also non- 

 motile species, but the most important examples are the typhoid, 

 paratyphoid, cholera and dysentery organisms. In typhoid and 

 paratyphoid fever the agglutination test is used as an aid in diag- 

 nosis of the disease by testing patient's serum against known 

 cultures, and the test with known serum is important in the iden- 

 tification of cultures of any of these bacteria. Agglutinins are 

 comparatively stable substances although they decompose 

 rapidly at 70 to 75 C. When dried they keep for a long time. 

 In Ehrlich's theory, the agglutinins are classed as receptors of 

 the second order, along with the precipitins. 



The Phenomenon of Agglutination. Clear fluid blood serum 

 to be tested for specific agglutinins is diluted with broth or with 

 salt solution to make mixtures containing one part of the serum 

 in 5, 10, 20, 40, 80 and 160 parts of the mixture. This is con- 

 veniently done by means of the Wright capillary pipette, or 

 graduated pipettes may be employed. To each dilution of serum 

 an equal amount of a very young (preferably two to six hours 



