82 SOME MINUTE ANIMAL PARASITES 



and have escaped as bacillary forms into the lumen 

 of each Malpighian tubule. After the seventh day 

 the organs of the tick develop very rapidly, and there 

 is much difficulty in observing the change of the 

 bacillary forms into the typical spirochsetes. But 

 two methods seem possible. In the first case fusion 

 of two or more bacillary forms may occur. In the 

 second case growth in thickness and simple elonga- 

 tion of the bacillary form produces the spirochaete, 

 and all the observations made seem to show that 

 this is by far the commoner method. 



The freshly hatched (and infective) nymphs of 

 either Argas persicus or Ornithodorus moubata are 

 very small indeed. If they are kept at a tempera- 

 ture of about 35 C. for some five or six days and 

 then dissected, it is found that within their intestines 

 there are usually many ovoid bodies, some bacillary 

 forms and a very few fully developed spirochsetes. 

 Experiments with such nymphs have shown that 

 they are very infective, and that animals bitten by 

 them, provided that the Malpighian fluid enters the 

 wounds, rapidly develop spirochaetes in their blood. 



Another interesting fact is that the ticks born of 

 infected parents grow up and become mature, and 

 are capable of transmitting the spirochaetes to their 

 eggs, so that the third generation of ticks may be 

 born infected. Hence there is the constant danger 

 of repeated hereditary infection to be considered in 

 any preventive measures relating to tick fevers. 



While the life-cycle of Spirochceta duttoni, the 

 parasite of African tick fever, is now well established, 

 that of S. recurrentis, the agent of European and 



