May, 1913. 



KNOWLEDGE. 



199 



by longitudinal fission. 

 The micronucleus is first 

 seen to divide into two, 

 splitting, as it does so, the 

 flagellum into half, so 

 that each of the two new 

 micronuclei has a strand 

 of the flagellum attached 

 to them. The splitting of 

 the flagellum then pro- 

 ceeds through the whole 

 length, the nucleus divides 

 into two, and by fission 

 in the protoplasm, the 

 organism becomes two 

 separate individuals, usually 

 of unequal size. The re- 

 production phase probably 

 has a far more compli- 

 cated cycle than this, how- 

 ever, even when repro- 

 duction in the blood of the 

 host is only considered, to 

 which the above descrip- 

 tion refers: but beyond this fission-method 

 of reproduction nothing is yet sufficiently 

 definitely known to need mention here. In 

 the alimentary canal and salivary glands 

 of the tsetse-fly, the reproduction phase of 

 trvpanosomes is exceedingly complex. 



The remarkable diversity in size and 

 shape that is found in trypanosomes of 

 any one species living in 

 the blood of an animal is 

 striking. They may vary 

 from slender organisms of 

 great length, possessing 

 highly developed undulat- 

 ing membranes, and long 

 free flagella, to quite 

 short, stumpy organisms 

 entirely wanting both these 

 appendages. What the 

 complete significance of 

 this series is we are at 

 present unable to say, 

 but some are probably 

 younger individuals, and 

 it seems likely that the 

 stumpy type are of a more 

 resistant kind than the 

 long type, since it is they 

 that are most numerous in 

 the blood when the host 

 is fighting the disease, or 

 when drugs are given to 

 the animal that render its 

 blood unfavourable to 

 the development of the 



By permission of Professor Mincliin and The Cambridge University Press. 



Figure 205. 

 Trypanosoma gambiense from blood of rat. X 1,000. 



(Smear fixed out with osmic acid vapour, and stained by C-iemsen. A slender, 



astumpy, and an intermediate form are seen. From plate illustrating Professor 



Minchin's paper in Parasitology, I. No. 3. 



* 



' " mi 1 1 1 1 , 1 1 1 



Natural size. 



1 11111 iiuniiii 11 1 in 



Magnified 13 diameters. 



liy permission o/ The Tropical Diseases Bureau, 



Figure 206. 

 Glossina palpalis Rob-Desv. The tsetse fly 



A good representation of the resting fly, but in life the palpi would 1 



Fi 



appressed and light would not be visible between them From a photo 



graph by I)r. W. M. Graham, Director of the Medical Research Institute. 



I.agos, S. Nigeria. 



trypanosome. Figures 204 

 and 205 show various types 

 of the same organism. 



Distribution. 



Trypanosomes occur all 

 over the world, and those 

 found infecting wild 

 animals in nature, are, as a 

 rule, quite specific to a par- 

 ticular host, and so far as 

 can be observed, perfectly 

 harmless to it, but there 

 are some which infect 

 man and animals, and are 

 highly pathogenic. Such, for 

 instance, is Trypanosoma 

 gambiense, the parasite 

 that produces Sleeping 

 Sickness. It is pathogenic 

 to all animals as well as 

 man. T. brucei, the try- 

 panosome that is so deadly 

 to the cattle and domestic 

 animals in Africa, gives rise to the disease 

 called Nagana or Fly-sickness; but it is 

 harmless to man, for it is unable to exist 

 in his blood.* An example of a trypano- 

 some that is harmless to its host is to 

 be found in T. lewisi. This trypanosome 

 is quite specific to rats, and though it may 

 swarm in the blood, so far as can be 

 seen, it has no harmful 

 effect on them, and as soon 

 as the infection has reached 

 a certain stage the number 

 of trypanosomes steadily 

 decreases in the blood, 

 finally disappearing alto- 

 gether, and leaving the rat 

 quite immune to a second 

 infection. 



A marked contrast to 

 this state of affairs is found 

 in the case of the trypano- 

 some of sleeping sickness. 

 Here, at no time in the 

 course of the disease in man 

 and many animals, are 

 the trypanosomes ever very 

 numerous, and though 

 their deadly effect may 

 be highly manifest in the 

 infected animal, their 

 presence in the blood 

 may be exceedingly diffi- 

 cult to detect, owing to 

 the extreme scarcity of 

 the parasites. 



* Since the above was written it has been stated, positively, that the cases of sleeping sickness in Nyasaland are due, not to a specific trypanosome called '/'. rhotUsiense. 

 but that this trypanosome ('/'. rliodesiense) turns out to be none other than T. brucei, i.e., the parasite that produces Nagana. (See paper by Sir I). Bruce and others, Royal 

 Society's Proceedings, Biological Section, April 7th, 1913). This shows how indefinite much of our knowledge of these organisms still is. For all there is to the contrary, 

 we may very well find ere long, that one half of what are looked upon as distinct species, are one and the same organism, altered slightly, it may be, by its adaptation to 



different environments. 



