206 Mutation in Micro- Or ganisTUS 



It should be noted that it is the kinetonucleus only which has been 

 removed from these organisms. The blepharoplast (end-knob, or basal 

 granule) and the rest of the locomotory apparatus remain intact^ 



Werbitzki endeavoured to obtain a race of Trypanosomes with 

 kinetonuclei by further treatment of the race from which this organ 

 had been removed. The parasites were treated with various dyes, 

 and passed through various animals (rats, guinea-pigs, rabbits) ; but 

 the results were not always the same. In one case, passage through 

 50 animals, and treatment with dyes, left the strain quite unaltered. 

 In another case, however, it was found that 7 % of the Trypanosomes 

 had acquired kinetonuclei at the 16th passage: and this percentage 

 increased during siibsequent passages, until at the 27th practically 

 every individual possessed a kinetonucleus. How the kinetonuclei were 

 " regenerated " was not determined. Microscopically, the individuals of 

 the new race did not differ in any way from normal Trypanosomes. 

 But it was found that their new kinetonuclei were susceptible to the 

 action of drugs which were without effect upon ordinary organisms. 

 For example, the kinetonuclei in the new race were removed by the 

 action of arsacetin — a drug which has no action in this respect on 

 normal Trypanosomes. 



An important question now arises as to the exact way in which the 

 kinetonucleus is removed from the strain of Trypanosomes which has 

 been subjected to the action of dyes of a certain sort. Werbitzki 

 suggested that its disappearance might be accounted for in three 

 different ways. First, the kinetonucleus might have been destroyed 

 by the dye, or eliminated from the organism ; secondly, it might have 

 fused with the trophonucleus ; thirdly, it is possible that the kineto- 

 nucleus has really not been removed, but its apparent absence is due 

 to the fact that it no longer takes up chromatin stains in the usual 

 way — owing to the action of the drug — and therefore is invisible in 

 microscopic preparations. The second and third suppositions were 

 shown by Werbitzki to be unsupported by any direct evidence. He 

 inclined to the supposition that the kinetonucleus had been destroyed 

 in some way. He figured, moreover, dividing forms of the Trypano- 

 somes in which one daughter individual contained a kinetonucleus, 

 whilst the other contained none. The suggestion therefore seemed 

 justified that the new race arose in this manner — by an irregular 

 distribution of the organ during division. No definite conclusions in 

 this respect were arrived at, however, by Werbitzki. 



1 This is stated on the authority of Dr v. Prowazek, to whom the strain was submitted 

 for a careful cytological examination. 



