C54 H. M. WOODCOCK. 



when examining or inoculating them; they always seemed to 

 be free from anything of this kind. 



Technique. — All my permanent preparations are in the 

 form of smears made on slides. As a rule, tlie thinner the smear 

 the better the result. In the case of very stout trypanosomes it 

 happens occasionally that they are rather flattened out if the 

 smear is too finely drawn ; but in thick smears the parasites 

 are often not well stained by the Komanowsky method, being 

 too blue in appearance. As regards smears of the cultural 

 forms, I experienced some difficulty at first, on account of the 

 expression-liquid (the medium containing the parasites), of 

 which the drop to be smeared consisted. This was quite clear 

 in the fresh condition, "but formed a sort of coagulum after 

 fixation, which stained very readily. Hence the trypanosomes 

 appeared to lie in a layer of substance, stained reddish, which 

 was often somewhat dense immediately around them. This 

 coagulated layer was much more noticeable in smears made 

 from the first kind of tubes than it was when I used the 

 second kind, to which salt-citrate solution was added. The 

 only means of obviating the trouble was to make the film as 

 thin as possible and to take care that no stain was deposited 

 on the slide. 



Fixation. — Most of my preparations have been fixed 

 with osmic acid vapour ; the few smears not so fixed were of 

 little value as regards the trypanosomes. I make use of a 

 4 per cent, solution of osmic acid, placed in the bottom of a 

 stain-tube, to which two or three drops of acetic acid are 

 added. The slide to be fixed is placed in the tube as quickly 

 as possible after the film has been drawn. A fairly deep or 

 thick glass ring in the liquid at the bottom of the tube 

 prevents the slide itself from getting wet. Slides are left in 

 contact with the vapour from twenty seconds to half a minute, 

 the shorter time particularly in the case of a smear from a 

 culture. After fixing, the slide is placed in absolute alcohol 

 for fifteen to thirty minutes, according to convenience. If the 

 smear is to be stained by the Romanowsky method, it is not 

 advisable to leave the slide in absolute alcohol for much 



