THE RAT TRYPANOSOME 805 



modification of Giemsa's stain (p. 774) : it is specially useful for staining the 

 trypanosomes of Nagana and Mai de Caderas. 



Levaditi advises drying the blood films in the air and then fixing them in 

 alcohol-ether. After fixing, the films are stained first in a saturated aqueous 

 solution of Bismarck-brown and washed, and then stained for 2 minutes in 

 Unna's polychrome blue diluted with an equal volume of water, washed, 

 dried and mounted in balsam. 



When the number of trypanosomes in the blood is small, thick films should 

 be spread on slides and the haemoglobin dissolved out either by Ross' or Le 

 Dantec's method (p. 772). Laveran recommends fixing in absolute alcohol 

 and dissolving the hsemoglobin in a 1 per cent, solution of acetic acid. Dutton 

 and Todd aspirate a drop of blood and a drop of citrated normal saline solu- 

 tion into a capillary tube with a bulb ; the fluids are mixed and the tube 

 sealed in the flame and centrifuged ; the red cells collect in the capillary part 

 of the tube, and above them at the lower part of the bulb is a layer of leuco- 

 cytes with which the parasites are mixed and this is used for examination. 



For the study of the cytology of trypanosomes the following is the only method 

 which, according to Salvin Moore and Breinl, gives satisfactory results. 



Fixation. Coat a slide with a thin layer of glycerin- albumin and spread a drop 

 of blood over it, before drying dip the slide into a strong solution of Flemming's 

 solution for 510 minutes, wash in alcohol of progressively increasing strength up to 

 absolute alcohol then treat with iodine and iodide in 80 per cent, alcohol and finally 

 in 30 per cent, alcohol. 



Staining. Stain with Heidenhain's iron-hsematoxylin containing a few drops of 

 a solution of lithium carbonate. 



Cultivation. Attempts have been made to cultivate Trypanosomes outside 

 the body and reference will be made to the results later in the chapter. The 

 medium used is blood-agar : either Novy and MacNeaPs or Nicolle's may be 

 employed (p. 799). Mathis recommends ordinary nutrient agar to which, 

 after liquefying and cooling to 59 C., 1-2 parts of defibrinated blood 

 (rabbit, rat, guinea-pig, ox or horse) are added : the mixture is heated to 

 75-80 C. for half an hour, then solidified on the slope. Whatever the 

 medium there must be a certain amount of water of condensation at the 

 bottom of the tubes and into this the infected blood is sown. India-rubber 

 caps should be slipped over the mouths of the tubes to prevent the medium 

 drying up. 



1. Trypanosoma lewisi. 1 

 The rat trypanosome. 



This parasite was discovered by Gros and Chaussat in the field mouse, mole 

 and black rat, and has been found by Lewis, Crookshank, Danilewsky, Laveran 

 and Mesnil and others in Mus decumanus, M. rattus, M. refuscens, Cricetus 

 frumentarius, etc. It occurs in a large percentage of rats all over the world. 



The parasite is transmitted by the rat flea, [Ceratophyllus fasciatus, and by 

 other fleas] and by the rat louse, Hcematopinus spinulosus (Prowazeck). 



[The normal method of transmission is that the ripe, infective form of the 

 Trypanosome the final form of the developmental cycle which it passes 

 through in the flea -is regurgitated from the stomach of the flea into the 

 wound made by the proboscis of the flea during the act of feeding. Rats 

 can be infected by devouring infected fleas but this is not the usual method 

 by which the transmission of the Trypanosome from rat to rat is effected by 



1 The trypanosome of the rat is often described as Herpetomonas lewisi (Kent). This 

 description is inaccurate because the fundamental characteristic of the genus Herpeto- 

 monas (type H. muscce domesticce) is the absence of an undulating membrane (vide 

 ante}. 



