53° 



Relapsing Fever 



Ornithodorus savignyi is chiefly a parasite of the camel and only occasionally 

 bites man; Ornithodorus moubata is essentially a human pest. 



The eggs of these ticks hatch in eight to fourteen days. The larval stage which 

 has six legs is spent in the eggs and the creature that emerges is usually a first 

 nymphalinston, which has eight legs. After hatching it remains inactive for 

 several days, then becomes very active and ready to suck blood. As it grows it 

 becomes voracious, distending itself with blood, then dropping off, hiding itself 

 for a time, molting, then being ready to feed again. This continues for a number 

 of months, the ticks molting four times before passing from the nymph to the 

 adult stage. 



Ornithodorus moubata is a common inhabitant of the native African huts 

 along the caravan routes. To avoid it and escape relapsing fever R. Koch in his 

 African expedition camped near but not in the villages, and avoided the native 

 houses. It lives in the cracks in the mud walls, in the thatch, in the mats and 

 sometimes simply upon the ground where its small size and dull color make it diffi- 

 cult to see. From these hiding places it crawls at night and like a bed-bug 



Male Female 



Fig. 205.— Pediculus pubis, Phthiriusinguinalis or crab-louse. X 17. (From 

 Beattie and Dickson's "A Text-book of General Pathology," by kind permission 

 of William Heinemann, Publisher.) 



attacks the sleeping host. When handled it feigns death, remaining quiet for 

 so long a time that it is hard to believe it alive. 



The Ornithodorus savignyi is less adapted to the requirements of the spiro- 

 chseta than its relative. Brumpt* found that the spirochEeta did not pass 

 through the eggs of O. savignyi to subsequent generations, and that the inf ectivity 

 of the tick itself soon was lost. The spirochastae remain indefinitely in O. mou- 

 bata, and are passed through their eggs to at least three generations. It is, 

 therefore, difiicult to be certain that any particular tick is uninfected unless its 

 progenitors be known. 



The spirochseta pass from female to the ovum and infect the young nyniphs as 

 such. The granules observed in the eggs of infected ticks, also occur in those of 

 non-infected ticks and have nothing to do with the spirochseta. 



II. Lice 



Lice are apterous insects formerly classed in the order Hemiptera, but now 

 placed in a separate order, the Anoplura. Two genera, and three species are 

 common upon human beings. 



I. Pediculus (Linn, 1758). In this genus there are two species: 



I. Pediculus capitis (de Geer, 1778). This is the head-louse. It is of a 

 gray color. The abdomen is composed of eight and not of seven seg- 

 ments as was stated by Piaget, and is blackened along the edges. The 



* "Precis de Parasitologic," 1910, 538. 



