\ATURE OF SUBSTANCES CONCERNED 7.V .{GGLUTL\ATH>\ 177 



The union of agglutinin with receptors in bacteria is a chemical reac- 

 tion, and is quantitative. Before agglutination occurs sodium chloride 

 must be present as it enters into the combination. The amount of bac- 

 teria in the emulsion used to test the amount of agglutinin must, there- 

 fore, be known. An emulsion one hundred times as dense as another 

 would require one hundred times as much agglutinin to give an equally 

 complete reaction. Agglutinin acts upon dead bacteria. 



Many things affect the agglutinable substance in bacteria. Grown 

 in bouillon for three days at 37 C., bacilli requires three times as much 

 agglutinin to give an equal reaction as if grown at 37 C. for one day. 

 This difference is partly due to bacterial substance passing out into 

 the culture medium, which combines with the agglutinin. 



Heat diminishes the agglutinability of bacteria when above 60 C. 

 Dreyer found that if a twenty-four-hour bouillon culture of bacillus 

 coli required 1 part of agglutinin to agglutinate it, then if heated to 

 60 C. it required 2.3 parts; if to 80 C., 18 parts; if to 100 C., 24.6 

 parts. He found the surprising fact that long heating of the culture 

 restored its ability to be agglutinated by smaller amounts of agglutinins. 



Heated thirteen hours to 100 C., the culture was agglutinated by 

 4 parts. Dreyer's explanation of this result is that agglutinin-fixing 

 substance is dissolved out by the prolonged heating. 



Heating the serum above 60 C. injures the agglutinin slightly, above 

 70 C. greatly, and above 75 C. destroys it. Weak and strong acids 

 agglutinate bacteria while medium acidity does not. Alkalies inhibit 

 agglutination. 



The nature of agglutinoids and the means by which they inhibit agglu- 

 tination is at present little understood. It is important to remember that 

 in concentrated serum agglutination may fail because of their action, while 

 in higher dilutions of the serum agglutination may take place readily. 



The growth of bacteria in fresh blood or its equivalent inhibits the 

 development of agglutinable substance in bacteria. Bacteria should 

 not be grown on such media when they are to be used in agglutination 

 tests. Even ascitic fluid broth has some effect. 



Group Agglutination. Many varieties of bacteria have among the 

 different substances composing their bodies some of which are common 

 to other bacteria which are more or less allied to them. These sub- 

 stances all exciting agglutinins we have such a serum acting on a 

 number of varieties. These agglutinins are called, therefore, group 

 agglutinins. If a typhoid or paratyphoid serum possess a high degree 

 of activity i. e., ability to agglutinate even in large dilution it may 

 happen that with lesser dilution it may also agglutinate the two related 

 bacilli. Thus, in two cases the infecting paratyphoid bacilli type B 

 were agglutinated 1:5700; typhoid bacilli, however, only 1:120, while 

 paratyphoid bacilli type A were not agglutinated at all. In two other 

 cases I observed an agglutination of paratyphoid type B with a dilution 

 1:40, while typhoid bacilli were agglutinated with 1:300 and over. 

 Korte has frequently observed that typhoid sera agglutinate not only 

 typhoid bacilli, but also one or both varieties of paratyphoid, even 



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