SPIROCHiET^ 369 



the same laboratory. There are certain differences between 

 these spirochetes of human relapsing fever, and several distinct 

 varieties (6r species?) are recognized. We shall consider them 

 as varieties of Sp. recurrentis. 



Spirochaeta Recurrentis var. Duttoni. — This is the spirochete 

 of Congo tick fever discovered by Button and Todd in 1904. It 

 is about o.45/i in thickness and 24 to 30^ in length. The organism 

 has been cultivated by Noguchi^ in ascitic fluid containing sterile 

 tissue and covered by paraffin oil. The African tick fever caused 



Fig. 143. — Spirochaetae of relapsing fever in blood of a man. {After KoUe and 



Wassermann.) 



by this organism is one of the most fatal of the relapsing fevers. . 

 The tick remains infective for a very long time and also transmits 

 the infection to its offspring through the egg. Other insects,^ 

 fleas 'and lice, are also capable of transmitting the infection. 



Spirochaeta Recurrentis var. Rossii (Kochi). — This organism 

 occurs ill the blood of relapsing fever of East Africa. It resembles 

 Sp. duttoni very closely. Noguchi obtained cultures readily in 

 ascitic fluid containing sterile tissue. 



Spirochaeta Recurrentis var. Novj^.' — This organism is 



more slender than the two preceding varieties, measuring about 



' Journ. Exp. Med., 1912, Vol. XVI, pp. 199-210. 

 2 Nuttall, Johns Hopkins Hasp. Bull., 1913, Vol. XXIV, pp. 33-39. 

 ' Novy and Knapp: Journ. Inf. Diseases, igo6, Vol. Ill, pp. 291^-393. 

 24 



