HEALTH AND DISEASE OF POULTRY 583 



ease-producing bacteria, picked up from the yard or roosts. By this 

 last means, if the organisms are particularly virulent, the disease 

 may pass through an entire flock, eventually killing all. If the range 

 is a large one, there is always danger from the fowls picking at the 

 bodies of their dead companions when these are left to decay on the 

 premises. 



The Treatment of Fowl Cholera. The treatment of fowl chol- 

 era may be carried on by protective inoculation or by medication. 

 It is an interesting fact that the fundamental work of Pasteur upon 

 protective inoculation in fowl cholera about 1880-82, was the first 

 attempt to produce by use of artificial "cultures" immunity against 

 a communicable disease, and was the basis of all later work in this 

 field, the valuable results of which, at the present day, we see in the 

 protective inoculation for diphtheria, lock-jaw (tetanus), cerebro- 

 spinal meningitis, and several other diseases. 



Pasteur ascertained that by inoculating fresh cultures of the virus 

 of fowl cholera he could, in almost even 7 case, produce the disease 

 in fowls so inoculated. He learned also that, if the cultures for in- 

 oculation were not used when fresh but after exposure to the air, 

 they might not produce the disease, for they seemed to have lost a 

 part of their virulence. Moreover, the extent to which they lost their 

 virulence appeared to correspond directly with the time during 

 which they had been exposed to the air. Thus Pasteur obtained two 

 grades of attenuated or weakened cultures, one of which was very 

 weak, the other, somewhat more powerful; yet neither so virulent 

 as the fresh cultures. But the important part of this discovery was, 

 that after a fowl had first been inoculated with the weakened cul- 

 tures, it could be subsequently inoculated with the virulent culture 

 without harm resulting; whereas, if the fresh culture had been 

 given first, it would surely have killed the bird. Hence the inocu- 

 lation of the weakened cultures had caused the formation, in the 

 body of the fowl, of certain substances (anti-bodies) that were able 

 to protect the bird against the stronger virus which was introduced 

 later. These anti-bodies, or immune bodies, appeared to neutralize 

 the poison produced in the body, by the organism of the unattenu- 

 ated culture, and thus to prevent the bird from having the disease 

 in a severe form. This was dependent upon the fact that the blood 

 of the inoculated bird had undergone some change that gave it a 

 protective value. 



Naturally, this method of Pasteur's for treating or preventing 

 cholera (producing active immunity), was not a very practical one 

 for the use of the poultryman: First, because it was a difficult 

 matter, requiring a laboratory to prepare the inoculation material; 

 and second, because each bird required several inoculations before 

 it was sufficiently protected to withstand the unattenuated culture. 

 For this reason, although the method has been of immense value to 

 mankind, in that it has shown the way to other methods of produc- 

 ing protective inoculation against communicable diseases, it has 

 proved of slight practical value to the poultryman, who, for the 

 treatment of his birds, requires a more simple and direct method. 



