244 ANIMAL PARASITES 



motility, and do not form spores. There is a single terminal 

 flagellum. They are stained with reasonable ease by plychrome 

 methods, especially Giemsa, but not by Gram's method. They 

 measure from 10 to 40/1 in length and about i/* in breadth. 

 Coils vary from 6 to 20. The American type is smaller than the 

 rest. 



FIG. 77. Spirilla of relapsing fever from blood of a man. (Kolle and 



Wassermann.) 



Transmission. The known tick which transmits these organ- 

 isms becomes infective in one week after biting a patient and 

 remains so all its life; its young are also infective. The types of 

 disease vary but little. In all these is a relasping fever with 

 periods of apyrexia in between. During the fever the spirochsetes 

 are swimming free in the blood and disappear in the afebrile 

 interval. 



Cultivation. They are cultivated in the manner given for 

 Trep. pallidum by Noguchi, by adding citrated, therefore de- 

 fibrinated, blood to serum or ascitic-fluid-fresh-tissue-agar. They 

 breed true to type. They remain alive several days under 

 favorable artificial conditions but cannot be cultivated after 



