SPOROZOA 467 



The Anaplasma marginale does not stain readily with the 

 usual anilin dyes, but can be demonstrated easily by a stain 

 such as Giemsa's. Heidenhain's iron hematoxylon also gives 

 good results. It may be seen even in the living cells as a refrac- 

 tive marginal granule. 



Pathogenesis. The disease produced has an incubation period 

 of sixteen to sixty days. The specific organisms may be first 

 demonstrated from the spleen; later they become abundant in the 

 blood. As many as 30 per cent, of the cells may be infected. The 

 first evident reaction is irregularity and poikilocytosis of the red 

 blood-cells, followed by more or less polychromasia and fragmenta- 

 tion. The serum does not seem to acquire any hemolytic proper- 

 ties. The febrile periods in the disease coincide with the presence 

 of the greatest number of marginal points in the corpuscles. Cattle 

 are susceptible to artificial infection. It is believed by Theiler 

 and his coworkers that the primary symptoms of disease in Texas 

 fever are due to Piroplasma bigemina, but that the secondary 

 symptoms are due to this Anaplasma marginale, which requires 

 a longer incubation period. 



Transmission. The organism is transmitted through the tick 

 (Boophilus decolor atus) . 



THE. GENUS LEUCOCYTOZOON 



Protozoa somewhat resembling the malarial parasites have 

 been found in the white blood-corpuscles or leukocytes in birds 



Fig. 207. Hepatozoon perniciosum, a leucocytozoon from the blood of 

 a rat: a, Free parasite; 6, parasites in the mononuclear leukocytes (adapted 

 from Miller). 



by several observers, and in the domestic fowl and the dog in 

 Tonkin by Mathis and Leger. They are not known to be of any 

 economic importance. 



