INHERITANCE IN TRYPANOSOMES 689 



nuclear and bi-nuclear trypanosomes ; therefore the power of 

 movement cannot depend on the kineto-nucleus. This name, 

 accordingly, becomes a little inappropriate but it is advisable to 

 retain the term, as it is now generally used to denote the smaller 

 and more densely staining nucleus of trypanosomes. This is an 

 excellent example of the danger of attributing functions to organs 

 on purely morphological grounds, nearly every writer having 

 assumed that the kineto-nucleus was the locomotor centre of the 

 trypanosome. 



Werbitski conducted experiments to ascertain how long a 

 mono-nuclear race of trypanosomes would persist when living, 

 generation after generation, in normal mice. In the first 

 series the blood of the fifteenth successively infected mouse 

 showed only mono-nuclear trypanosomes ; in the sixteenth 

 mouse a few parasites were found in which the kineto-nucleus 

 had reappeared ; after a few more generations (passage through 

 six to eight mice) the race had become indistinguishable from 

 the normal bi-nucleate type. But this apparently normal race 

 possessed a very striking peculiarity : when exposed to the 

 action of substances having no effect on the morphology of 

 normal trypanosomes, the kineto-nucleus again disappeared. 

 For example, acetylatoxyl, arsacetin and tryparosan — substances 

 which have no effect on the nuclei of normal trypanosomes — all 

 caused the disappearance of the kineto-nuclei from the recovered 

 race. The newly acquired kineto-nucleus is thus shown to be 

 more labile than the normal nucleus. 



In some cases the mono-nuclear race of trypanosomes pre- 

 serves its peculiarity, without any further treatment, during an 

 indefinite period. Laveran 1 found that a race of T. brucei that 

 had been exposed to the action of pyronin was still mono-nucleate 

 after having passed through 130 animals successively (a period 

 extending over more than one year). 



There are two possible explanations of the origin of the 

 mono-nuclear races of trypanosomes. Kudicke 2 having found 

 that a small percentage of trypanosomes that had never been 

 exposed to the action of any drug did not possess a kineto- 

 nucleus, it has been suggested that these mono-nuclear races 



1 Laveran (191 1), "Contribution a l'Etude du Trypanosoma \brucei sans 

 Blepharoplaste de Werbitski," Bull. Soc Path. Exot. 191 1, pp. 233-9. 



2 Kudicke (191 1), "Die Wirkung orthochinoider Substanzen auf Ratten- 

 trypanosomen," Centralbl. f.\Bakteriologie, vol. lix. pp. j 182-5. 



