210 MICRO-ORGANISMS AND DISEASE [chap. 



zone, and then a transparent marginal part. In stab culture 

 the line of inoculation becomes marked as a white line 

 made up of more or less confluent yellowish-white droplets ; 

 on the surface of the stab is a thin, irregularly outlined 

 plate ; in streak cultures the growth appears after two or 

 three days as a yellowish-white band with irregular or 

 knobbed outlines, thin in the centre and margin, thicker 

 and brownish in the intermediate parts ; on potato the 

 microbe grows only at higher temperatures, 28°-38° C. 

 It grows slowly and forms a waxy grey-white film. 



By inoculation of minute quantities, a drop of culture 

 into the subcutaneous tissue, or by feeding of fowls, rabbits, 

 mice, or pigeons with culture, the disease is easily repro- 

 duced. In guinea-pigs and sheep it produces a local abscess 

 at the seat of inoculation. 



By keeping broth cultures for some months Pasteur has 

 succeeded in producing by inoculation of fowls a local 

 oedematous inflammation ; the animals became only slightly 

 affected, but recovered and showed themselves refractory 

 against a second inoculation. Pasteur thought that the 

 influence of the oxygen of the air produced the attenuation ; 

 it is now proved, however, that this is not so (Kitt), but that 

 Pasteur had impurities (accidental microbes) in his broth 

 cultures, which at first attenuated the baciUi of fowl cholera 

 and, as time went on, altogether suppressed these ; hence the 

 broth cultures of Pasteur after the lapse of some months 

 proved barren of all pathogenic action. 



Pasteur has shown that by injection of large quantities of 

 broth cultures from which the bacilli of fowl cholera have 

 been previously removed by filtration a transitory illness can 

 be produced, and that such animals show themselves after- 

 wards refractory against inoculation with virulent material. 

 Marchiafava and CeUi showed that the microbe passes from 



