Natural Infection, Anatomical Changes. 421 



remains alive for a long time on the dirty floors of damp stables, 

 in musty food and straw, and from there reaches the buccal 

 cavity of young animals. Healthy animals may become in- 

 fected by contact with affected ones, by licking them, thereby 

 introducing diseased products (shreds of pseudo-membranes 

 hanging from the mouth, nasal secretions) into their mouths. 

 The easy transmissibility of the disease has been fully estab- 

 lished by Dammann, since he watched a healthy calf which was 

 placed in a stable between two affected calves, become affected 

 in five days. 



The disease attacks young sucking calves exclusively, which 

 sometimes become affected as early as on the third day after 

 their birth. The great susceptibility of the young can probably 

 be explained by the loose and delicate consistency of the 

 epithelia of the mucous membrane. The susceptibility of the 

 newly born may also be increased by any other physical weak- 

 nesses, the residue of the milk remaining in the mouth of such 

 animals being especially adapted for the localization and propa- 

 gation of the virus. Injuries of the buccal mucous membrane, 

 such as the eruption of the milk teeth, may constitute the prin- 

 cipal entrance for the infective agent. 



Anatomical Changes. The autopsy reveals on the mucous 

 membrane of the mouth and pharynx, various sized and coalesc- 

 ing croupous membranes, which extend higher than the eleva- 

 tion of the surrounding tissue. They are several centimeters 

 thick, sharply circumscribed, dirty gray or brown in color, 

 ragged on the surface, and firmly adherent to the underlying 

 tissues. Ulcerations also occur with thickened borders and 

 ragged bases; between these lesions the mucous membrane is 

 greatly swollen, reddened, the submucosa shows serous infiltra- 

 tion. Preferred places for the formation of these pseudo- 

 membranes are, the inner surface of the cheeks, the hard palate, 

 the borders of the tongue, the parts surrounding the frenum 

 of the tongue, the gums, the soft palate and the pharynx. In 

 sQjne cases the mucous membrane over a considerable area and 

 in its entire thickness changes to a yellowish-gray, brittle, fetid 

 mushy mass. The muscles of the tongue may also be necrotic 

 under the affected parts of the mucous membrane to a greater 

 or lesser depth, the destructive process on the hard palate 

 may even extend to the bone producing caries, and changing 

 it to a soft mushy mass. Similar changes occur also on the 

 lower parts of the nasal cavity, on the larynx and in the trachea, 

 where they may affect the cartilage. 



The lungs usually contain either dry or purulent, softened, 

 necrotic areas, which are surrounded by zones of catarrhal, 

 pneumonia, and sometimes also a purulent pleurisy may be pres- 

 ent as a result of perforation of such superficial, necrotic areas. 

 The small intestines reveal acute catarrh, whereas posterior to 

 the cecum sometimes pea-sized dirty yellow, dry deposits may be 



