THE AGGLUTININS 221 



In any culture of bacteria it will be found that some individuals 

 are more easily agglutinated than others. In the early cultures 

 in clumping serum the susceptible forms grow, but they sink to the 

 bottom in a dense network. The less sensitive forms also grow 

 from slight granules or a diffuse turbidity through the fluid. If 

 the subcultures are inoculated from this fluid, the change to the 

 non-clumping form occurs more quickly than if the masses were 

 used for the transfer. There is therefore a process of selection 

 of the non-clumping forms, and in time all the susceptible bacilli 

 become eliminated. It is this process, though in a more marked 

 form, that accounts for the increased virulence of the bacteria, 

 which is brought about by passage. For here all bacteria which 

 are not resistant to the bacteriolysins and to the phagocytic 

 action of the leucocytes will be killed off, and will not propagate 

 their species. We may therefore conclude on theoretical grounds 

 that virulent bacilli are those having (along with a potent toxin) 

 few receptors which can be attacked by amboceptor and opsonin. 

 We have seen that Pfeiffer and Friedberger's experiments do 

 not tend to corroborate this (in the case of amboceptor), but that 

 they cannot be regarded as conclusive. 



The increase in the virulence of the organism by cultivation in 

 immune serum has been generally corroborated, though Roger 

 found the opposite to occur when streptococci were cultivated in 

 antistreptococcic serum. 



The hamagglutinins occur in normal and in immunized 

 animals. Those in the latter call for no especial notice ; they are 

 developed after injection of red corpuscles side by side with 

 immune body, and their presence can be demonstrated if the 

 serum be heated or if the experiment be performed in the cold. 

 The normal agglutinins which one species may possess for the 

 red corpuscles of another species call for no special notice. 



The iso-agglutinins are, however, worthy of a short description. 

 They are common, and have been most studied in human blood, 

 and will be found to occur to a greater or less extent in most 

 specimens of human sera. The phenomena they produce are 

 entirely similar to those produced by a specific serum in a typhoid 

 culture. Under the microscope the corpuscles will be seen to run 

 together into masses which are quite unlike the ordinary rouleaux 

 of shed blood in that the corpuscles are approximated together 

 without any trace of definite arrangement. When a strong serum 

 is used the cohesive force may be so great that the corpuscles 



