SYSTEMATIC DESCRIPTION OF SPECIES. 97 



ing membrane, and multiplies by transverse division. 

 The blood of the mouse is not infective, nor was trans- 

 mission by fleas effected. It is apparently a harmless 

 parasite. 



Wenyon thinks it may be identical with the form 

 found by Borrel in mouse-cancer and perhaps with the 

 spirilla discovered in the rat by Carter. 



FIG. 73. Spirochaeta muris. (After Wenyon.) 

 SPIROCH^TA MINOR. 



(Spirillum minor, Carter, 1887.) 



Carter found in the rat, Mus decumanus, spirilla 

 (spirochaetes ?) measuring 5 to gft in length, and pos- 

 sessing four to eight curls. He describes them as 

 shorter and slenderer than Sp. obermeieri. They have 

 pointed ends, and exhibit movements of rotation, pro- 

 pulsion, and lashing. They disappear and reappear 

 in the blood of the rat, being replaced during their 

 absence by granular particles and filaments. 



SPIROCH^TES IN MOUSE-CANCER. 



Gaylord found spirochaetes constantly present in 

 mouse-cancers, both primary and secondary. They 

 were studied by Calkins, who describes them as 2.5 to 

 7.8/1 in length, o.6// broad, and possessing four to 

 thirteen curls. The ends are blunt and rounded, and 

 they have no undulating membrane or flagella. 



Borrel had previously observed these organisms in 

 1905. They are not causally connected with the 

 7 



