TRYPANOSOMA LEWISI 551 



It is as yet too soon to express any opinion on the ultimate effect of 

 these views. According to Schaudinn a trypanosomal spirillum consists 

 of a central thread which represents the posterior nucleus of the 

 trypanosome ; round this thread the undulating membrane is spirally 

 wound, and the principal nucleus is represented by minute chromatin 

 dots sometimes seen in the course of the spiral. Whether all spirilla 

 have this structure must be left for future investigation to determine. 

 Difficulties arise with regard to the significance of an undulatory 

 membrane as a spirillary characteristic and also with regard to the 

 terminal flagellum which Schaudinn himself found in Spirochsete pallida, 

 and which he had previously thought did not occur in protozoal spirilla. 

 It is possible that two groups of organisms have hitherto been classed 

 together under the name spirillum, and that one of these may still 

 have to be placed with the bacteria. 



Trypanosoma Lewisi. In 1878 Lewis described in rats in 

 India the occurrence of the parasite which now goes by his 

 name, and since that time this trypanosome has been found to 

 be very common in the blood of rats all over the world, though 

 the percentage of animals affected varies in different localities. 

 The condition is of great interest, as, though the infection runs 

 a very definite course, it is very rarely fatal ; in fact, many 

 observers have been unable to produce death by infecting even 

 large series of animals. There is, however, little doubt that a 

 fatal issue does occur sometimes in young individuals, especially 

 when these are infected with strains of the organism imported 

 from other localities. The trypanosome, which is actively 

 motile, is of the usual length but is somewhat narrow, and its 

 protoplasm does not contain any granules. It multiplies by 

 fission, of which Laveran describes two varieties. In one, the 

 organism splits longitudinally and gives rise to smaller individuals 

 than the parent. In the other, the trypanosome loses its 

 ordinary shape and becomes more oval; nuclear division, 

 which is often multiple, then takes place, and on subsequent 

 division of the protoplasm a number of small flagellate organisms 

 result ; these last may attain the full form and size before 

 dividing again, or they may divide when still small. When a 

 rat is infected by injection into the peritoneum active multi- 

 plication goes on in the cavity for a few days and then comes to 

 an end. Very soon after infection the organisms begin to appear 

 in the blood and there rapid multiplication occurs, the extent 

 of which is sometimes so great that the trypanosomes may seem 

 to equal the red blood corpuscles in number. The animal 

 usually shows no symptoms of illness. The infection goes on 

 for about two months, and then the organisms gradually dis- 

 appear from the blood. In the great majority of cases the rat 

 is now immune against fresh infection. If trypanosomes be 



