212 H. M. WOODCOCK. 



not inclined to regard this structure as a normal constituent 

 of the cell, — comparable, for instance, with an excretory 

 vacuole. They only describe its occurrence very rarely (fig. 

 42 c) ; their preparations showing it are of Trypanosomes 

 which were not in the blood, but in another medium, e. g. 

 serous, or cerebro-spinal fluid, and they consider that it 

 is an artifact caused by the imperfect fixation of such fluid, 

 in which, of course, the parasite is bathed. There are, 

 however, several considerations to be set against this view. 

 All the above figures are from blood preparations, and in the 

 Reports of the Sleeping Sickness Commission there are some 

 realistic figures of T. gambiense from the blood, in most of 

 which this vacuole is well marked.^ Moreover, Dutton and 

 Todd's figures (I.e.) of dividing stages of T. dimorphon 

 show clearly that an oval vacuole is present and also divides 

 (fig. 49 ii). Again, it is important to note that a similar 

 structure has been described in the case of parasites in their 

 natural (tolerant) hosts, and in what there can be no question 

 were absolutely normal conditions. Thus Leger (1. c.) de- 

 scribes a clear, oval space near the anterior end of Trypano- 

 p las ma, which, he says, probably represents a true vacuole, 

 and is not to be confused with certain rounded vacuoles that 

 sometimes appear in unhealthy individuals^; Hanna figures 

 a small vacuole in his Trypanosome from Indian pigeons 

 (fig. 16 g) ; and lastly, Schaudinn describes one or two large 

 ones in the indifferent forms of Trypanomorpha noctute, 

 near the apparently opposite, flagellate end be it 

 noted. Hence it appears almost certain that a vacuole, 

 probably excretory in function, may occur normally in many 

 Trypanosomes.^ 



^ The writer would add that he has seen some of these, and other 

 preparations of Mammalian Trypanosomes, in which the parasites appeared 

 perfectly normal and exhibited this vacuole. 



- Progressive vacuolisation on a large scale is often met witli in atypical 

 or abnormal conditions of the parasites (see below, p. 229). 



^ It may possibly be that the technique used by LaVeran and Mesnil is 

 not suited for demonstrating this particular point (see below, p, 217). 



