1912.] 



A Camel Trypanosoma 



567 



points of distinction. Here, however, it will not be necessary to measure a 

 great number of trypanosomes. In the case of other mammalian trypano- 

 somes, e.g., T. brucei, gambicnsc, fecavdi, rhodesiense, evansi, equiperdum, 

 equinum, ncmum, and congolcnsc exhaustive measurements are of little use in 

 diagnosis. 



The following example will illustrate very well both the uses and the 

 limitations of the measurement method. In papers dealing respectively 

 with the morphology of T. gambicnsc and T. evansi Bruce gives three curves 

 of T. brucei for purposes of comparison. The apices of the curves are at 18 

 20 /a, and 24 p respectively, a very considerable variation. Further, in dealing 

 with T. evansi, he claims that from a comparison of the two curves it is 

 possible to distinguish the two species from one another. In the case of 

 T. bntcei the bulk of the curve will be between 13 p and 35 a, with T. evansi 

 between 18 /a and 30 //.. A glance at the curves, however, will reveal the fact 

 that the real difference between the two trypanosomes as determined by the 

 biometric method is that T. evansi shows no forms; of less than 18 fx, in length. 

 In other words, if in the course of examining a slide a trypanosome is found 

 below say 15 /j, in length, the diagnosis cannot be T. evansi. Thus the ' 

 diagnosis has in reality turned upon the minimum measurements of the two 

 species. 



The measurements quoted for the different species of trypanosomes vary 

 with the observer, even although the staining and fixing methods are the same 

 in every case. This variation is due to a number of factors, the least important 

 of which is probably the technique employed in the actual measurement. 



It would appear from Miss Kobertson's recent work on T. gambicnsc* that 

 an endogenous cycle exists in the mammal, the duration of which is variable 

 and incalculable, the result being that the type of trypanosome predominating 

 in the peripheral blood is constantly changing. The date of the infection 

 has no constant connection with the course of the phenomenon. In each 

 cycle the change would appear to be from short to long forms, returning to 

 the short forms again before the temporary disappearance from the blood. 



To obtain an accurate conception of the dimensions of any trypanosome 

 it is plain that all the stages of such a cycle must be followed out, from 

 its commencement to its conclusion. Slides taken haphazard from time to 

 time are useless for comparative purposes, as practically any type of curve 

 may be obtained according to the stage of the cycle. The three curves of 

 T. brucei quoted above from Bruce's paper are an instance of this. In a 

 recent report summarised in ' Sleeping Sickness Bulletin 36 ' (vol. 4, p. 145), 

 Dr. Stephens lays great stress on the minute technique of measurement, and 

 * ' Roy. Soc. Proc.,' B, vol. 85 (No. 582). 



VOL. LXXXV. — B. 2 S 



