112 AGGLUTINATION 



each of the third row receives i loopful of typhoid bacilli, 

 each of the fourth row receives i loopful of paratyphoid B. bacilli, 

 All are once more placed in the incubator for two hours. 



a. If typhoid exists the agglutination titer in the second part of the test will become 

 weaker for the typhoid bacilli in the first row, and weaker for the paratyphoid B. bacilli 

 in the second and fourth rows. The titer in the third row remains the same. 



b. If paratyphoid exists, the agglutination titer for typhoid in the first and third 

 row becomes less, that for paratyphoid in the fourth row diminishes, while the titer in 

 the second row for paratyphoid remains the same. 



c. If a mixed infection exists, the agglutination titer in the first and fourth row 

 diminishes and in the second and third row remains the same. 



In this connection a few exceptions may be mentioned: 



A serum which is kept for a long time frequently loses part 

 Agglutinoids. or even all of its agglutinating titer. Whereas it formerly 

 agglutinated in the strength of 1:1000, it may now become 

 inactive in dilutions even of i : 10. The first thought that arises in explana- 

 tion of this is that the serum has perhaps degenerated and the agglutinins 

 were destroyed. If, however, further dilutions are made, i : 100 may show 

 mild, while i : 500 strong agglutination. This, first of all, demonstrates 

 that agglutinins are still present, although diminished in amount, and sec- 

 ond, that another substance has arisen which in the stronger concentrations 

 interferes with agglutination. A simple experiment explains this. 



If the test-tube containing the serum dilution i : 10 and the non-agglutinated 

 bacteria be centrifugalized, the serum removed and the bacteria mixed with a known 

 strongly agglutinating serum, it will be found that the bacteria have become inagglu- 

 tinable. Substances of certain kinds have combined with the bacteria and prevented 

 them from undergoing agglutination. These substances are strongly specific, acting 

 only upon homologous bacteria. Their origin can also be demonstrated. 



An agglutinating serum which is heated to 65 or 70 C. loses its agglutinating power 

 but the substance interfering with the subsequent agglutination has remained. Ehrlich 

 explains the situation as follows: He claims that agglutinins are built complexly; that 

 they possess a binding (haptophore) group by means of which they unite with the bac- 

 teria (agglutinogen) and a second group (ergophore or agglutinophore) by virtue of 

 which agglutination results. If serum is kept for a long period of time, or exposed to 

 high temperature, many of the ergophore groups are rendered inactive, while the 

 haptophore groups being more resistant remain and unite with bacteria. Agglutinins 

 possessing only their haptophore groups are known as agglutinoids. They combine 

 with the bacteria, and still do not agglutinate them, but at the same time prevent 

 other agglutinins from acting. If this old agglutinoid and agglutinin containing 

 serum is diluted, so few of both of these substances remain that the bacteria can 

 absorb both, allowing the relatively few agglutinins to manifest their activity. 



It is important to note in this respect that occasionally even a fresh, highly valent 

 serum will present a tendency toward interfering with the agglutination processes. 

 This is also explained by the existence of agglutinoids a fact as yet not definitely 

 proven. 



Another finding, only encountered in exceptional cases, is me existence 

 of the so-called non-agglutinable strains of bacteria. These give all the 



