40 ESSENTIALS OF BACTERIOLOGY 



animal and becomes attached to the cell receptors of the 

 second order by means of its haptophore group, the cell is 

 irritated and new receptors are formed. Further injection 

 of larger amounts of protein stimulate the cell to such an 

 excessive formation of these receptors that they are thrust 

 free into the blood-stream. 



A precipitin serum is a suspension of receptors of the second 

 order in blood-serum. 



The phenomenon of precipitation has found forensic 

 application in the identification of blood-stains. 



Agglutinins are bodies present in a serum which, when 

 added to bacterial cells, cause them to clump, and, if motile, 

 to lose their motility. They are specific when diluted, and 

 of value in diagnosis in such diseases as typhoid and Malta 

 fever. 



Agglutinins are formed in response to the stimulus given the 

 cells of a body by the union of antigenic cell-receptors with 

 receptors of the second order of the cells of the animal re- 

 ceiving the injection. Repeated injections stimulate the 

 cells to the formation of such excessive quantities of these 

 receptors that they are thrown from the cells into the blood- 

 stream. 



Agglutinins bear no relation to the degree of immunity, 

 and should never be used as an index to immunity. 



Cytolysins are bodies present in a serum which will dis- 

 solve or destroy cells (corpuscles, bacteria, etc.). 



They are formed in the same manner as the agglutinins, 

 except that receptors of the third order are involved. Recep- 

 tors of the third order have a double combining affinity. 

 One part attaches itself to the receptor of the cell injected, 

 and the other combines with complement. 



Complement (alexin or cytase) is a thermolabile, ferment- 

 like body found in all normal sera. 



Amboceptors, "substance sensibttatrice" fixateur, copula, 

 and desmon are names given to receptors of the third order. 



Cytolytic sera are of little use in medicine. Sera have been 

 prepared against staphylococci, pneumococci, streptococci, 



