46o MICRO-ORGANISMS AND DISEASE [chap. 



vibrios ; their cultural and other differences may, just as 

 was the case with the above oyster-vibrios, have been 

 acquired and established through the environment, through 

 their sojourn for some time under abnormal conditions. 



R. Pfeiffer, in a series of well-known papers published in 

 the Zeitschrift f. Hygiene und Infekt. during 1894 and 1895, 

 has established the important fact that the blood-serum of 

 guinea-pigs highly immunised by repeated intraperitoneal 

 injection of living cholera vibrios {see a former page) 

 possesses potentially specific immunising or germicidal 

 action m corpore, that is to say, when in a certain pro- 

 portion mixed with an otherwise fatal dose of cholera 

 vibrios and injected into the peritoneal cavity of a guinea- 

 pig, it kills the vibrios, and no disease follows, the animal re- 

 mains alive and well and is "passively immunised." This was 

 then extended by Pfeiffer also for the obtaining of " cholera 

 serum," i.e. of immunising serum, from the highly immunised 

 goat, and was shown to hold good also for " typhoid serum," 

 i.e. for a potential specific germicidal action of blood-serum 

 of animals highly immunised by intraperitoneal injection of 

 cultures of the typhoid bacillus against an otherwise fatal 

 dose of the typhoid bacillus. Several observers, I myself, 

 have been able to confirm — as indeed is easily done — 

 Pfeiffer's fundamental discovery. 



Bordet (Annales de rinstitut Pasteur., June, 1895) and 

 recently Durham (Proceedings of the Royal Society, January 

 23, 1896) show that also in vitro "cholera serum " shows a 

 definite separating action, inasmuch as when added in 

 definite proportion (sometimes alone, sometimes with 

 normal serum — Bordet, alone — Durham) to a suspension 

 of living cholera vibrios contained in a test-tube it makes 

 the vibrios become matted together in clumps, settling 

 at the bottom of the test-tube while the suspending 



