80 



POULTRY DISEASES 



of blood cells. One of these, a white-blood cell 

 (phagocyte), has taken up one of the germs. 



Mode of Spread. — Birds often contract this dis- 

 ease from others at shows, and when taken back 

 home infest the remainder of the flock and the 

 premises, or a bird recently purchased from an 

 infected flock, or eggs from an infected flock, 

 or chicks recently hatched in infected sur- 

 roundings, or infected droppings carried on 

 the feet of men and animals, from hen- 

 houses where the disease exists, or carried by 



streams or irrigation 

 ditch water, dried and 

 carried by the wind as 

 dust, or carried by wild 

 birds, may be the means 

 of introducing this dis- 

 ease among healthy 

 birds. Even insects 

 have been known to 

 carry the contagion. 

 Buzzards are common 

 carriers of this disease. 

 The germ of fowl 

 cholera retains, its power to produce disease for 

 weeks, and even months, about premises where it 

 has occurred, unless they be thoroughly disin- 

 fected. The germs have been kept in test .tubes, 

 experimentally, for two years and still proved to 

 be virulent, that is, still capable of producing dis- 

 ease. It resists, for a long time, both drying and 

 zero weather. 



Cholera may affect chickens, turkeys, ducks, 

 geese, pigeons and many wild birds. The period 

 of incubation (the time elapsing from the entrance 

 of the germs into the body of the bird until the 



Fig. 26. Blood Smear from Case 

 OF Cholera 



Showing red blood cells, throm- 

 bocytes, mononuclear leucocytes, 

 polymorphonuclear neutrophiles 

 and many of the polar staining 

 germs (Bacillus avisepticus) of 

 the disease. 



