﻿84 



Proceedings of the Royal Physical Society. 



material was, however, got in Eothesay Bay and the surround- 

 ings of Bute, through the courtesy of Messrs John and 

 Thomas Thorburn, of Eothesay. 



The number and condition of the trypanosomes in the 

 alimentary canal of the leech is subject to very considerable 

 variation, but I have only found one, out of over sixty leeches 

 investigated, that was quite free from these parasites. The 

 method of investigation has been as follows : — The leech is 

 cut open along its whole length, great care being taken not 

 to pierce the thin wall of the crop. As a matter of con- 

 venience and precaution, a small incision is first made at the 

 anterior end and the proboscis extracted. This ensures that 

 no possible contamination can have taken place through the 

 bursting of the crop or the intestine. After the leech has 

 been opened, the intestine, which is a long, thin tube extend- 

 ing through about the last third of the body, is either opened 

 in situ or is extracted from before backwards, care being 

 taken to nip the cut edges in a pair of forceps. The intestine 

 is then opened by means of a needle and its contents spread 

 out upon slides, which are either dried rapidly in air and fixed 

 in absolute alcohol, or are fixed, while still wet, by exposure 

 to osmic vapour, or to osmic and acetic acid vapour. The 

 stain employed was Griemsa's modification of the Eomanowsky 

 method, or Laveran's stain. Live preparations were made by 

 placing a drop of the fluid in the intestine on a slide, adding 

 a drop of physiological salt solution when necessary, and 

 immediately covering with a coverslip and sealing with 

 vaseline. It is well, if possible, to avoid adding the salt 

 solution, as the trypanosome remains more lively when 

 kept in its natural medium. The dark colour of the fluid 

 from the intestine, however, often renders observation 

 difiicult. 



The parasite usually lives under these conditions from 

 twelve to forty-eight hours, or even longer. Unfortunately, 

 the various changes in the trypanosomes seem to follow 

 each other very slowly ; so that while much valuable in- 

 formation is to be obtained from the study of the living 

 creature, the most patient observation only results in 

 following the individual through a few usually unimportant 



