58 



PEACTICAL PARASITOLOGY 



outer plasm is called the periblast ; it stains a light pink after pro- 

 longed immersion in Giemsa's stain. In cover-glass specimens, single 

 parasites are sometimes found, which have become crushed during 

 preparation in such a manner, that the thin inner plasma escapes 

 through rents in the periblast. This is sometimes observed in 

 T. theileri (the giant Trypanosome of cattle, which may attain a 

 length of 0'06 toO07 mm.), and is also seen, though with less frequency, 

 in smaller varieties. In these crushed examples, 

 the myonemes are readily made out by reason 

 of their darker colour, though their position may 

 be very much altered by the rupture of the peri- 

 blast. The term "myoneme" is misleading in 

 this case, as the fibrillse are not contractile, but 

 elastic, resembling the axis-fibrillsB. 



Fission forms are not observed with any fre- 

 quency among the parasites of fish, but they are 

 frequently found in rats and mice when the in- 

 fection is very severe. 



Fission takes place longitudinally, the prin- 

 cipal nucleus and the flagellar nucleus dividing 

 independently of one another. From the 

 flagellar nucleus of one of the daughter in- 

 dividuals a new flagellum is formed. This lies 

 so closely to the original flagellum, which is 

 retained by the second daughter individual, that 

 its presence can be detected only after very care- 

 ful examination. At a first glance it looks as 

 if the flagellum divided from its base upwards. 

 Colouring by Giemsa's method seems to show 

 that the division of the principal nucleus takes 

 place, as in the Coccidia, from within outwards 

 by the division, in the first instance, of an inner 

 body or caryosome (Prowazek, Liihe). But care- 

 ful study of damp-fixed cover-glass specimens 



coloured with iron-hsematoxylin shows that this effect is artificially 

 produced by the Giemsa stain, and that division takes place as a 

 result of a true mitosis (Kosenbusch 2 ). 



It has already been stated that Trypanosomes may be kept alive 

 for a certain time outside the body of their host. Their examination 

 is considerably facilitated by the fact that they may be cultivated by 

 Novy and McNeal's method upon blood-agar. 



FIG. 15. Diagram 

 of the organization of 

 Trypanosoma lewisi. 

 (After Prowazek, from 

 Braun.) Theaxis-fibrillse 

 are removed ; the " myo- 

 nemes " are dotted in. 



1 Short prefatory note in Arch. f. Protisienkunde, vol. xii, 1908, parts 1 and 2, 

 pp. 169. 



