44 



ANIMAI. THYPANOSOMIASES IN TUE ANGLO-EGYrTIAN SUDAN 



Uruces system 



of 



measureniiiit 



Animal 

 inoculations 

 and reactions 



(_'ultural 

 methods 



keaclinn 

 to drugs 



this we liave in Bnice's system. Under this system the trypaiiosomes are drawn at a 

 {^iven magnilicatioii (2000 diameters) and they are measured in a uniform way (i.e. with 

 calipers down the body keeping the points of the instrument rigidly in the middle) from 

 films, if possible, fixed and prepared in a uniform fashion — osmic fixation, Giemsa staining. 



From numbers thus drawn and measured the average size is obtained, and a maximum 

 and minimum length is stated also, charts giving curves of the distribution, by percentages 

 in respect to length, are prepared and the type thus graphically illustrated. 



Wo have here, then, a definite and simple method of morphological classification 

 which, following Bruce's system, is being carried out in these laboratories, and from 

 which clear statements of results can be obtained. 



It must be remembered that in this method there are some pitfalls and some 

 fallacies, but they can readily be avoided or taken into account, as, for instance, in the 

 comparison of trypanosomes from different animal sources. A comparison of tables from 

 the measurements of trypanosomes from a coimuon laboratory stock animal, such as 

 the rat, is preferable to the indiscriminate study of the relation of trypanosomes in 

 different classes of animals. 



It is well known that the inoculation of the same strain of trypanosome into various 

 animals is productive of certain differences in measurement, hence it is unwise to compare 

 new species without taking this into account. In these laboratories the most convenient 

 animal is the gerbil, but in general, any of the small rodents is, as a rule, a suitable 

 animal. So nmcii for morphological methods, on the whole simple and workable. 



In animal inoculations and reactions we have another exceedingly useful method 

 of distinguishing trypanosomes, but one that must be used with a somewhat open mind, 

 for we know from laboratory experiments that, by certain methods of transmission, we 

 can infect animals which have proved refractory to the original strain, and wc can do 

 this in a simple manner. Also, one sees how readily a strain, owing to laboratory 

 transmissions, sometimes varies in character and virulence. We are thus led to keeping 

 our distinctions, as far as animal reactions go, on broad general grounds, and to avoiding 

 the error of allowing overmuch importance to the i-efractory power or susceptibility of 

 occasional animals. Pathological changes in animals should also be viewed in the same 

 manner ; for instance, opacity of the cornea is not seen in every case of Surra in dogs. 



Cultural methods. These have not proved of very great value, for beyond the point 

 that various observers have been able to say that a certain trypanosome can be " grown 

 readily" or "cannot be grown" we can arrive at few more subtle distinctions; however, 

 so far, these methods do help us. But here again, the possibility of a trypanosome being 

 easily growable, or the reverse, according to its more immediate host environment, must 

 not be forgotten. Also, the preparation of media is dependent on individuals and different 

 supplies of blood serum — points well illustrated by the fact that some observers have been 

 able to grow known strains while others have failed. 



These conclusions will make us chary of jumping to definite conclusions under 

 this heading. 



The question of carrier is one probably of more importance in practical bionomics 

 than in differentiating trypanosomes, still it is also useful in this connection ; but an 

 acquirable suitability of carrier is as understandable as an acquirable susceptibility of host. 



Reaction to drugs, is a method at present of the most questionable importance 

 and of which little can be said except that it is unsatisfactory. Two drugs are being 

 used here in this connection, metallic antimony and Ehrlich's "GOG," but from experience 

 with various antimony and arsenic compounds, little can be hoped as yet from this method. 



