494 STUDIES IN IMMUNITY. 



on account of their rarity are obviously due to contaminating 

 organisms. It would seem that the surface of the culture medium, 

 which had been smooth and shiny, was uniformly roughened be- 

 tween these colonies, but the change is so very slight that it might 

 easily be overlooked. Even with a magnifying glass a layer of 

 bacterial growth could not be asserted to be present. But if a 

 drop of water is inoculated with a scraping from this surface, with 

 great care in avoiding the colonies of contaminating organisms, 

 and this water used to inoculate the buccal mucosa of a normal 

 hen, the disease is produced. 



This same fluid on microscopical examination shows an enormous 

 number of little granular elements which are at times slightly elon- 

 gated about 0.0002 of a millimeter in size, and are most frequently 

 united in compact zooglea masses. 



The culture may be transplanted and retransplanted indefinitely. 



The layer of bacterial growth that is formed is never thick enough 

 to be very evident. It is evidenced simply by a darkening and 

 roughening of the surface. At times, however, very luxuriant 

 cultures are obtained which show extremely small colonies or a 

 distinct outline limiting the area covered with growth. The Giemsa 

 stain is the best to demonstrate the organism. 



This organism, together with the one causing peri-pneumonia 

 of cattle, is probably the smallest that has ever been grown. It 

 generally reproduces the disease in a somewhat attenuated form, 

 to be sure, particularly when the buccal mucosa is inoculated. 

 The white plaques that appear in 2 or 3 days often heal rapidly, 

 but also frequently reappear later in the same place, and then 

 become more extensive. These lesions, although somewhat benign, 

 are of typical and undoubted specificity. 



Certain hens are refractory. Inoculation on the nictitating 

 membrane is always severe and always followed by characteristic 

 symptoms, such as edema of the eye, and thickening and redness 

 of the third eyelid, which shows the chronic nature of the disease. 

 To demonstrate our infecting experiment on the nictitating mem- 

 brane more conclusively, and to avoid any objection that this 

 infection is simply due to a contagion, or a natural propagation 

 of the disease in the laboratory, and not an artificial infection, we 

 have passed a thread through each nictitating membrane in a nor- 



