380 



Incubation Period. Five to six days, the infection 

 reaches a maximum in about ten days. Spirochaetes 

 also occasionally occur in the blood of Mus decumanus, 

 and, it is stated, in the blood of bandicoots (Nesocia 

 bandicota). 



6. Sp. muris, var. virginiana, in a wild rat in 

 Virginia, 3*5 by 0*25/4. Easily transmissible by inocu- 

 lation to wild rat, the incubation period being seven 

 to fourteen days. 



7. Sp. theileri. Occurs in cattle in Africa 

 (Transvaal and Cameroons). According to some the 

 same spirochaete exists also in horses and sheep. 



Symptoms. As Piroplasma sp. and T. theileri are 

 also commonly present, it is difficult to ascribe the 

 affection and death solely to the spirochaetes. 



Morphology. The spirochaetes are actively motile, 

 20-30/4 long. Small forms, 8/4, also occur. 



Pathogenicity. Besides cattle, sheep are suscep- 

 tible. 



Mode of Transmission. The larva of the infected 

 mother tick M. decolor atus (blue tick), transmits the 

 disease. The incubation period from tick bite is about 

 a fortnight ; and as this tick passes all its life, three to 

 four weeks, on cattle, it is possible for the larval tick to 

 re-infect itself when adult, from the beast it has infected 

 when itself in the larval stage. 



The blood of immune animals is still infective 

 (cp. P. parvum). 



8. Sp. anserina. The cause of a fatal disease in 

 geese in the Caucasus and in Tunis. 



Symptoms. : (i) Fever, (2) diarrhoea, (3) acute 

 tenderness of the feet. Death occurs in about a week. 

 The mortality is about eighty per cent. 



Blood Examination. The spirochaetes occur in 



