XVI] VIBRIO AND SPIRILLUM 461 



fluid becomes clear, and that after some time the 

 motility of the vibrios becomes impaired and ceases, al- 

 though living colonies can still be cultivated from them. 

 Durham shows this action to take place also when " typhoid 

 serum " is added to a suspension of typhoid bacilli. 



We shall speak of Pfeiffer's germicidal action of the 

 cholera serum in corpore as of Pfeiffer's test, of the Bordet- 

 Durham separation test in vitro as of the Bordet-Durham test. 



As stated just previously, the fundamental fact discovered 

 by Pfeiffer as to the pronounced germicidal action of 

 "cholera serum'' or "typhoid serum'' on cholera vibrios 

 and typhoid bacilli, respectively, is well established. Now, 

 Pfeiffer shows by numerous experiments that the " cholera 

 serum," that is, the blood-serum of animals highly im- 

 munised by living vibrios of an undoubted cholera origin, 

 possesses this pronounced germicidal action in corpore on 

 all samples of vibrios — several hundred — which he and 

 others got hold of from undoubted cases of Asiatic cholera, 

 but that it fails to exhibit this action on vibrios of doubtful 

 derivation, like the various water vibrios, the vibrio Nord- 

 hafen, &c. — that is to say, on vibrios which are not directly 

 and notoriously derived from undoubted cases of Asiatic 

 cholera — and he therefore feels justified in concluding that 

 any species of vibrio which submitted to Pfeiffer's test 

 succumbs is a cholera vibrio, any species which does not 

 succumb to Pfeffer's test is not a cholera vibrio. The same 

 is applied by Pfeiffer to the typhoid test mutatis mutandis. 

 Bordet and Durham imply through their test in vitro a 

 somewhat similar conclusion ; but though their test was of 

 positive differential value in the case of the cholera serum 

 and cholera vibrio it was not so unequivocal, according to 

 Durham, in the case of colon serum and colon bacillus. 

 Koch has shown (Zeitschr. f. Hygiene, vol. xii.) that if in 



