Natural Infection. 105 



otic outbreak occur as a rule through infections of the soil, 

 the causative agent in some localities acquiring a strong viru- 

 lence through unknown influences, or they may he due .to a 

 diminished resistance of the animals. As local enzootics fre- 

 quently develop first among deer and black game the moist soil 

 of the forests appears to be especially favorable for the propa- 

 gation of the bacteria and for the change in their virulence 

 mentioned above. The warm spring weather is particularly 

 favorable for the development of the bacteria. During this 

 period the disease occurs most frequently among cattle. 



The virus which originates from the soil retains its in- 

 creased virulence for a certain time in the body of the animals, 

 and this may even be increased further. The blood is highly 

 infectious in the latter stages of the disease, and during this 

 time the blood as well as other body fluids and excrements may 

 also infect other animals, and in this way the enzootic may 

 continue to spread in a contagious form. (Bollinger observed 

 an infection in a steer which died from pneumonia within 54 

 hours after the ingestion of 1 gram of feces from a calf affected 

 with an acute form of the disease.) After a certain time these 

 enzootics which do not as a rule extend over large territories, 

 usually subside very probably as the result of an attenuation 

 of the virus which takes place in the meantime ( Carrougeau 

 observed a gradual attenuation of the virus from repeated re- 

 inoculations of cattle). 



The cornstalk disease or corn fodder disease which occurs among 

 cattle in America, especially in the middle and upper Mississippi 

 Valley, is also supposed to be caused by an ovoid bacterium, and to 

 be identical with hemorrhagic septicemia of cattle. This disease usually 

 occurs in the fall and early winter after the animals are turned into 

 the cornstalk fields. It is characterized by a very rapid course. The 

 autopsy reveals numerous hemorrhages in the internal organs, espe- 

 cially in the serous membranes. Eecently, however, Moore showed 

 that the disease was not of an infectious nature, but was due to toxic 

 substances (according to Mayo, potassium nitrate) which are sometimes 

 present in large quantities in the stalks, and which are responsible 

 for the intoxication. As a matter of fact the disease may be actually 

 prevented by cutting the stalks early and only feeding them after they 

 have been carefully cured and removed from the field. 



Anatomical changes. The autopsy reveals a marked 

 hyperemia of the internal organs as well as fresh hemorrhages 

 in the serous and mucous membranes, and in some of the 

 organs, especially the lungs and muscles. The spleen has either 

 a normal appearance or contains circumscribed bloody areas; 

 the liver and kidneys show cloudy swelling. The other ana- 

 tomical changes vary in the different cases. 



In the edematous or exanthematous form the subcutaneous 

 connective tissue of the head, the throat region and the neck, 

 show a gelatinous infiltration, which may in some places be 

 studded with hemorrhages. The serous infiltration may extend 



