210 AGGLUTINOID 



even opaque, then granular, and finally flocculent. It presents a 

 most extraordinary resemblance to the clumping of an ordinary 

 culture, but a microscopic examination will show the flocculi 

 consist of amorphous granules instead of bacteria. It has been 

 suggested that it is due to a clumping of cilia which have passed 

 through the filter (Nicolle), but the phenomenon has since been 

 observed in the case of the pneumococcus (Panichi) and other 

 non-flagellated organisms. The agglutinable substance is thermo- 

 stable. It does not appear to be given off in all cases, and some- 

 times all attempts to get Kraus's reaction are unsuccessful. 



This substance is the antigen of agglutinin, and our nomen- 

 clature would be more uniform if we were to call it agglutin and 

 its antibody anti-agglutin, but the terms are too firmly fixed to be 

 altered. We shall call it agglutinable substance, or agglutinogen. 



The fact that heated serum still agglutinates shows that alexin 

 or complement plays no part in the process, but we have already 

 explained how we know that the molecule of agglutinin possesses 

 an ergophore or zymophore group. This group, as is the case 

 with the corresponding groups of the toxins and complements, is 

 less resistant than is the haptophore group, and is destroyed at 

 70 to 75 C. The substance left is called agglutinoid, and is 

 analogous to toxoid and complementoid. Its existence is demon- 

 strated thus : Heated serum (or serum which has been kept for a 

 long time) is added to a culture of bacteria. No agglutination 

 takes place. The bacteria are then centrifugalized off and placed in 

 a strongly agglutinating serum, but are found not to clump. It 

 is evident, therefore, that the bacteria have their receptors 

 occupied by some substance which prevents the union of the 

 agglutinin. The agglutinoid has combined with the agglutinogen, 

 and excludes the unaltered agglutinin. 



In some cases at least agglutinoids, which have a stronger 

 affinity for bacteria than has normal agglutinin, may be present. 

 In this case, if bacteria be added to a mixture of the two sub- 

 stances, no agglutination occurs. The pro-agglutinoids (as they are 

 termed, the expression being taken from the prototoxoids) seize 

 on the agglutinable substance in the bacteria before the 

 agglutinin can do so. If to this mixture more bacteria be added, 

 more pro-agglutinoid will be taken up, until it is all exhausted, 

 and then any fresh bacteria that are added will be clumped. 

 This is one explanation of a phenomenon which is fairly frequently 

 observed (if looked for) in the clinical diagnosis of typhoid fever, 



