5ii2 MICRO-ORGANISMS AND DISEASE [chap. 



and break up into globules and granules. This germicidal 

 action of the cholera serum in corpore has been already 

 spoken of as Pfeijfer's test, it does not take place in vitro. 

 The same law holds good more or less for other microbes : 

 erysipelas, typhoid, Finkler, colon, prodigiosus, so that it 

 seems to possess general application, but it must be added 

 that it is by no means so absolute as is represented by 

 Pfeiffer. 



Bordet and Durham (Joe. cit ) show that a " potent serum " 

 acts specifically (specialised, Durham) on its particular 

 microbe or races of microbes also in vitro, inasmuch as in 

 definite quantity and definite time a potent serum causes a 

 more or less perfect separation, aggregation, and precipita- 

 tion and loss of motility of the microbe contained in a 

 suspension, without however destroying the microbe, for 

 even long after the microbes have separated active cultures 

 can still be produced with them. 



The germicidal action of the serum as shown by Pfeiffer's 

 test is on the whole but not without exception specific, 

 that is to say it is only exerted against the microbe with 

 which the animal had been actively immunised. As 

 is now well known an animal, say a guinea-pig, can be 

 protected intraperitoneally against a fatal dose of the living 

 microbe, e.g. vibrio of cholera, by previous repeated intra- 

 peritoneal injections of the living or of the dead microbes 

 (Klein), but this immunisation is of a comparatively tem- 

 porary nature, and does not yield specific germicidal serum 

 unless often repeated and with considerable doses. 



A certain resistance, non-specific in nature, of the tissues 

 against microbic action has been produced in various ways : 

 thus Wooldridge showed that the injection of thymus extract 



