H. Bayon 
139 
(1906) in S. duttoni, and by Novy and Knapp (1906) in S. duttoni and 
novyi. 
This terminal filament is not visible in all specimens of 8. recur- 
rentis, duttoni, or novyi. It is quite possible that Schellack is right in 
considering it only present in young specimens, which have but lately 
divided. This would be an observation more in favour of the 
transverse division of spirochaetes, which moreover can often be seen 
taking place in blood-films if patiently examined by dark-ground 
illumination. Miss Mackinnon (1909, a) observed in two cases apparent 
longitudinal division but in eleven the division was apparently 
transverse. It could not be said with certainty, except in one 
instance, that these transverse divisions were not the final act in 
a longitudinal division. Therefore it is apparent that if both modes 
of division occur, the transverse is by far the more common in blood. 
The same seems to hold good for the divisions of Treponema pallidum 
observed in Noguchi’s cultures. 
Fig. 1. 
Fig. 3. 
Fig. 1. Side view of ring. 
Fig. 2. Front view. The arrow indicates the direction of rotation. 
Fig. 3. Erythrocyte of mouse, to show comparative size. 
On comparing my notes on the three strains of spirochaetes which 
I studied, I cannot say that I noticed any special mode of progression 
which was typical for any one species. The screw-like and the lashing, 
trypanosome-like movements, as also more or less flattened spirals, 
occurred in all the strains according to circumstances and the degree 
of infection in the animals experimented upon. 
A most peculiar appearance in 8 . recurrentis was seen on several 
occasions in the blood of mice which had been infected with relapsing 
fever blood. It consisted in the rolling up or encircling of the 
spirochaete round what appeared to be an exceedingly thin membrane 
containing small refringent granules, which were actively moving. It 
was difficult to recognise these forms as spirochaetes, because an 
