2l6 THE " PRO-ZONES " IN AGGLUTINATION 



a temperature of 72, followed by filtration. The action of the two 

 is specific. If the filtrate be injected into animals, the serum 

 which results clumps ordinary typhoid bacilli well, but has little 

 action on those from which the separable substance has been 

 removed. The serum obtained by injection of the bacilli deprived 

 of separable substance is weaker, and has an equal action on the 

 bacilli whether normal or heated and deprived of soluble substance. 



It is evident that the subject is a complicated one, and this 

 is even more clear from the researches of Dreyer and Jex-Blake 

 on the agglutination of B. coli by its specific serum. Investigating 

 first the behaviour of the bacilli when heated, they found, as other 

 observers had done, no alteration at 60 C., but a sudden diminu- 

 tion in the power of undergoing agglutination when heated to 

 70 C. This, of course, is usually ascribed to the complete or 

 partial destruction of the agglutinogen, though this explanation is 

 incomplete, since (as Eisenberg and Volk had previously found) 

 the bacilli which do not clump will still combine with agglutinin. 



But Dreyer and Jex-Blake found that the agglutinability is 

 partially or completely restored by prolonged heating to 100 C. 

 After exposure to this temperature for a period of from two to 

 thirteen hours, the susceptibility of the bacilli to the serum might 

 be as great, or almost as great, as at first. This is an extra- 

 ordinary fact, and one for which no adequate explanation is 

 forthcoming. The only parallel is the behaviour of megatheriolysin 

 (a bacterial hsemolysin), also investigated by Dreyer. This is 

 destroyed, or at least rendered inert, at 60 C., and reactivated at 

 the boiling-point. 



These authors also adduce evidence to show that the " zones of 

 inhibition," or "pro-zones," described by Eisenberg and Volk as 

 occurring with heated serum, cannot be explained by the assump- 

 tion of the presence of " agglutinoids " with a high affinity for 

 agglutinogen. The evidence against this view is briefly this : If 

 it were true, the more the serum were weakened by the heat 

 (i.e., the greater the production of agglutinoid), the larger should 

 be the zone of inhibition, and vice versa. This they found not 

 to be the case, for a serum which had not been appreciably injured 

 by the heat might have a large zone of inhibition. They also 

 found exactly similar zones in investigating agglutination caused 

 by means of acids, in which case, of course, nothing of the nature 

 of agglutinoids could occur. Thus, in a series of experiments it 

 was found that when orthophosphoric acid was added to a definite 



