which have been maintained of such organisms as T. gambiense, 
T. evansi and T, dimorphon in all the usual laboratory' animals, there 
has never been any suggestion that a new t\-i3e has been created. 
Increased and decreased virulence may and does occur, but this is less 
marked, under normal maintenance of the strain, than was hitherto 
supposed, and there is always a tendency to reversion towards the 
original state. 
B\- means of these two factors the nine remaining trjpanosomcs 
can be conveniently grouped as follows: — 
A. Trypanosomes, pathogenic towards most domestic animals, 
and producing a rapidly fatal infection in the usud' 
laboratory animals: 
id) monomorphic, of large and fairly constant size, from 
20(1 to 35/i in length, and carrying a distinct free 
flagellum. T>pc - - 7 ’. evami. 
{J}) di* (ir polymorphic, of very \ariable size, occurring in 
at least two forms: (i) ‘short,’ measuring from lO/i 
to 15/x in length, and devoid of a free flagellum; 
(2) long, which may attain 35i«, and bearing a 
variable length of flagellum. Intermediate forms 
also occur. Type— T. dimorphon. 
Trypanosomes, pathogenic to certain domestic animals, and 
without apparent effect when inoculated into the usual 
laboratory animals (monkey, dog, rabbit, guinea-pig, rat and 
mouse). An imperfectly studied group, which includes 
T. nanum, T. vivax and T. cazaldoui. 
tf'ni Blis grouping to be sufficiently exact for the 
^ worker in the Tropics. Unless the organism 
mornh Ic eahng shows any striking peculiarity in either 
o one oMh" -ore than assign it 
to one of these groups. 
doi"th«T!’ 
and we referrertTtirsrasT 
the reasons set out below. ' ' ^ 
