AKIMAL MICRO-PARASITES. 601 



blood of a field mouse, and he also mentions that Chaussat found 

 minute " nematodes " in the blood of a black rat. 



Wittich discovered in the blood of hamsters whip-like bodies with 

 lively movements. They resembled frog's spermatozoa, possessing 

 a thick portion continued into a long lash-like thread. Wittich 

 considered them identical with the organisms described by Lewis, and 

 they also were observed in apparently healthy animals. Koch later 

 met with the same organisms. 



Like Lewis, the author found that the blood of the common 

 brown rat in England appeared to quiver with life, and that the 

 parasites were extremely difficult to examine until their movement 

 was arrested for a moment or they became imprisoned in the serum 

 areas. After examining with variotis powers, from a i dry 

 to a -^-g o. i. of Powell and Lealand, the author came to the 

 following conclusion : — That they are polymorphic, presenting for 



Fig. 240. — A Monad in Rat's Blood. The organism is represented at partial 

 rest with its posterior filament impinging on a corpuscle, and showing the 

 undulating longitudinal membrane, the long flagellum, and the refractive 

 spherules in the granular protoplasm ( x 3000). 



the most part slightly tapering bodies which terminate at one end in 

 a stiff, immotile, acutely-pointed flexible filament or spine-like process, 

 and at the opposite end are provided with a long flagellum, whUe, 

 longitudinally attached, a delicate undulating fin-like membrane can 

 be traced, which starts from the base of the posterior filament, and 

 becomes directly continuous with the flagellum (Fig. 240). 



With careful illumination the body is found to be distinctly 

 granular, with one or more highly-refractive spherules. When the 

 rapid movement is arrested the undulating membrane is distinctly 

 visible. The best opportunity occurs for seeing this when the 

 organism comes to partial rest with its stiff filament against a 

 corpuscle, as if to obtain a point d'appui, whUe lashing its flagellum 

 in all directions (Fig. 241, b). At other times, when the parasite has 

 impinged with its posterior extremity against a corpuscle, or the 

 stiff fllament is apparently entangled in debris, the movements of 

 the organism give one the idea of its endeavouring to set itself free. 



