338 TEXT-BOOK OF BACTERIOLOGY. 



New generations could even be obtained at will, all of which pre- 

 served the same attitude. Whenever Pasteur inoculated such ma- 

 terial into the breast- muscle of chickens, for instance, a mere local 

 inflammation ensued, which generally became rapidly circumscribed 

 and terminated in the expulsion of the altered tissue by suppura- 

 tion, without any other disturbances. 



Pasteur's interpretation of this phenomenon as the consequence 

 of the unobstructed access of oxygen has been disputed and refuted 

 by many authors. Cultures of these bacilli on oblique gelatin (hence 

 with a purely superficial growth) and propagated in the same way 

 from generation to generation, always retain their virulence, for 

 which reason some authors ascribed the attenuation to the action 

 of the breeding heat. 



Pasteur's experiments of attenuation were followed by his sig- 

 nificant experiments with artificial protective inoculation. l3y means 

 of this inoculation, at first with a greatly- weakened infectious sub- 

 stance (" le premier vaccin ") and subsequently with a much stronger 

 (" le deuxieme vaccin "), even highly-susceptible animals, such as 

 fowls and pigeons, may be secured against infection. A practical 

 utilization of this fact has been attempted, but veterinarians gener- 

 ally are not in favor of such a procedure. 



The results of microscopic examination, artificial cultivation, and 

 transmission prove that the bacilli of chicken cholera are the sole 

 cause of the plague. 



How do the micro-organisms enter the animals and cause the 

 peculiar disease ? 



Experiments and careful observations of the natural conditions 

 have furnished a satisfactory answer to this question. It is pretty 

 certain that, in most cases, infection ensues from animal to animal 

 and is brought about by bacilli contained in the excrements of d iseased 

 individuals, being reabsorbed with the food by previously healthy 

 birds. 



Successful inoculations also show that the poison may be trans- 

 mitted, too, from slight lesions of the integument etc. The vital 

 properties of the bacillus rendering it probable that it may thrive, 

 or at least continue to exist, outside of the animal body, the occasion 

 for infection is easily afforded. 



The micro-organisms having once effected an entrance, they mul- 

 tiply rapidly, and thus cause the group of symptoms appearing in the 

 course of the affection. The chickens frequently sink at once into a 

 state of great debility and apathy ; they remain motionless in one 

 spot, as if paralyzed, double themselves up with bristling feathers 

 into a rigid ball, close their eyes, and fall into a death-like sleep 



