Pathogenebis. 11 



soon ensues, it is usually characterized by its insiduous 

 and chronic course. The first few months after infec- 

 tion frequent intermittent febrile attacks occur. But 

 when the illness is alleviated a little, patients as a rule 

 acquire the power of resistance against the virus, and 

 fiebrile attacks decrease in number until they return to 

 normal. It need hardly be mentioned that the virus is 

 retained in the body for a considerable length of time. 



The chief pathologic change of the disease consists in 

 a marked decrease of the red blood corpuscles. Also more 

 or less noticeable lesions are found in the heart, liver, 

 spleen, kidneys, lymph-glands, bone-marrow, etc. Mor- 

 tality is between 30 9^ and 70 9^, according to the condi- 

 tions of the disease, climate, care of patients, etc. 



Blood examinations of the affected horses reveal 

 that three to four millions of red corpuscles are present 

 in 1 c. m. m., and in advanced cases less than one million 

 in so much blood; that is, less than one-seventh of the 

 number of red corpuscles in found normal blood (six to 

 seven millions). If the red corpuscles of the patient's 

 blood be precipitated to the bottom of a graduate, its 

 coagulation being prevented, the corpuscular layer mea- 

 sures less than one-tenth the whole volume, while in 

 normal blood it is more than four-tenths. 



B. Etiology. 



In order to detect the causative agent of the disease 

 the blood and viscera of patients were subjected to all 

 possible microscopical and culture methods with negative 

 results. It was found that the virus passes through 

 Berkefeld's and Chamberland's filter. It should be re- 

 marked that the apparatus had been tested with Bacil- 

 lus prodigiosus beforehand and had been proved really 



