46 



:he weather. Young l)irds and individuals of the finer Ijreeds are especially 

 susceptible. 



Fowl Diphtheria usually appears here with the unfavorable weather of the 

 fall and early winter. In one night, a large number of fowls may become af- 

 fected with catarrh, following which some fowls may become roupy, while 

 others recover in a short time. 



The experiments to transfer the disease by means of the pathologic se- 

 cretions and excretions seems to contradict to a certain extent, our opmion about 

 the way natural mfection takes place. To explain this, we must bear m mind the 

 fact that the causal organisms may be present in the pathologic secretions, 

 etc., in large numbers, and in a very virulent form, whenever the germs are 

 located on the surface, or in the highest layers of the epithelial membranes. 

 (See fowl No. 8, and the result of isolating the bacilli from its pathologic pro- 

 ducts). 



The Roup bacilli are not always localized in one place like the Klebs- 

 Loeffler bacillus, which produces human diphtheria. The organisms causing 

 Roup penetrate into the deeper and submucous tissues, and become the cause 

 of phlegmonous processes and secondary catarrh of the adjacent mucous mem- 

 branes and glands. In such cases, the roup bacilli are seldom present in the 

 slimy, putrid secretions and pseudo-membranes. Further, the roup bacilli 

 have often entirely disappeared from the pathologic secretions, or are mixed 

 with many other 'bacterial species. This phenomenon occurs not only in 

 chronic cases of natural infection, but also takes place in fowls which have 

 been inoculated with the roup bacillus. 



The pathological products themselves are sufficient, owing to their local- 

 ization, their consistency, and the histological changes they cause, to produce 

 the continuance of chronic catarrhs. Finally, as already stated the roup bacilli, 

 enclosed in the cheesy masses, lose their vitality. 



The fowls experimented with did not suffer from common colds, which 

 must play an important part in the natural disease. As our experiments show, 

 it is easier to infect healthy birds by keeping them a long time with diseased 

 ones (5 out of lo became diseased) than by direct inoculation of pathologic 

 products on the experimental animals. The explanation of this is that fowls 

 kept with diseased ones for a long time, are exposed to the possibilities of an 

 infection, and at some time during this exposure the natural resistance of the 

 bird is lowered, or sonic unfavorable condition allows infection to occur. 



