140 
Haemojlagellates, etc. 
APPENDIX. 
Since the. above review was written three papers dealing with try¬ 
panosomes and allied flagellates have been published which it will be 
necessary to refer to shortly here. Bruce and his collaborators (1909) 
have repeated Kleine’s experiments (see p. 107) with T. gambiense and 
G. palpalis, and have found that this fly is infective after 16, 19, and 22 
days subsequent to its ingesting the trypanosome. This discovery only 
goes to show that during this period T. gambiense remains alive and 
retains its virulence while in the fly, but it by no means proves it under¬ 
goes a developmental cycle. There is at present too great a tendency to 
conclude that certain trypanosomes must pass through developmental 
cycles in tsetse flies, for we find that in a leading article on Bruce’s 
recent work in the British Medical Journal (May 15th, 1909, page 1200) 
it is stated, “ the fact that trypauosomes develop in tsetse flies may now 
be said to be established.” We are not told what is meant by the term 
“ develop,” presumably the writer means a sexual cycle; as far as we are 
aware there is no proof that trypanosomes pass through any such cycle. 
To say then that T. gambiense has a developmental cycle in G. palpalis 
is pure assumption and the loose usage of the terms “ develop ” and 
“ developmental cycle ” are misleading and are to be strongly depre¬ 
cated. 
We will now consider the possible explanation of the long period of 
non-infectivity of tsetse flies: (1) From our knowledge of the life-cycles 
of Herpetomonas and Crithidia it is conceivable that T. gambiense, in 
addition to the well-known flagellate stage, is ingested by G. palpalis in 
a non-flagellate form, as has been described by Salvin-Moore and Breinl, 
and that this stage of the parasite becomes a flagellate during the period 
of non-infectivity ; it is however not known whether these forms occur in 
the peripheral blood of sleeping sickness cases. Whether this is so or not, 
it would quite well explain the long period of non-infectivity of the flies. 
(2) The parasites after being ingested by the fly undergo a sexual cycle, 
perhaps after Schaudinn’s plan for T. noctuae, and then make their way 
up to the proboscis of the fly. We have however shown above that this 
cycle is most improbable. (3) The trypanosomes, after remaining from 
14 to 16 days in the stomach of the fly, make their way to its proboscis 
without passing through any sexual cycle; during this period they 
may undergo equal and unequal longitudinal division. These seem to 
