44 SPlROCliiETES 



disease. Indeed, the tiny unfed nymphs are very infective, and 

 on account of their small size are particularly dangerous since 

 they are not easil}^ detected. The ticks do not usually transmit 

 the parasites by means of the beak but deposit a bit of infected 

 excrement l)esitle the wound they make; from here the spiro- 

 chaetes make their way into the blood, aided by the scratching 

 which follows the tick l)ite. However, when the tick is kept 

 for a few days at a temperature of 95° F. the salivary glands as 

 well as nearly all other organs become infective, and the disease 

 may then be transmitted in the usual insect manner, by injection 

 with saliva. The relapsing fever of Abyssinia and Somaliland 

 is transmitted by a closely allied tick, Ornithodorus savignyi. 

 African tick fever is said to have been imported into Persia, 

 where it is transmitted by 0. tholosani. The complete life cycle 

 of SpirochcEta duttoni is shown diagrammatically in Fig. 7. 



The other types of relapsing fever spirochsetes do not appear 

 to have such definite and invariable transmitters. Nicolle and 

 his fellow workers have shown that in Algeria the head and 

 body lice are undoubtedly the means of spreading the disease. 

 In experimental work they have shown that there is a rapid tem- 

 porary disappearance of the spirochsetes from the body of the 

 louse after they have been sucked with blood from an infected per- 

 son; during this time they are presumably in the granular stage. 

 After about eight days the spirochsetes reappear and are abundant 

 in the body cavity of the louse for some 12 days before they 

 finally disappear for good. The lice are infective while spiro- 

 chsetes are jyesent in their usual form, and also just before they 

 reappear at the end of eight days. It is by crushing the louse 

 and allowing the juices from its body cavity to contaminate the 

 wound that infection is obtained. 



In experimental work in Algeria a man experimented upon 

 was bitten several thousand times by infected lice without con- 

 tracting the disease, but one louse crushed, and the body fluids 

 placed on the conjunctiva, caused the disease to develop. The 

 same result would undoubtedly have occurred if the crushed 

 louse had come in contact with a wound of the skin. 



In some cases the spirochsetes are transmitted through the 

 eggs 1o the next generation of lice, just as in the case of ticks and 

 the African disease. The louse has been shown to be the trans- 

 mitter of relapsing fever in India also. 



