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another direction, the proportion was but one out of 34 although the latter 
district contained many piggeries, etc. 
The number of spirochaetes found in the emulsion of the kidneys of the 
positive nine rats varied very considerably. In the first positive rat from the 
town they were very numerous, as many as three to eight spirochaetes being 
found in one field and many in groups, whilst in the next positive rat from 
the same spot only very few were found in a whole preparation. In four of 
the positive rats from the country they were moderately numerous, whilst 
in the two others there were only three or four spirochaetes found in stained or 
fresh films. In the last rat examined large masses of spirochaetes were found. 
The length of each rat examined was noted, and I am of the opinion that 
spirochaetes are more likely to be found in the half grown, in rats of about 
seven to eight inches long, than in very large or very small rats. My reasons 
for forming this opinion are that all the positive rats were about this size, 
and secondly it is reasonable to suppose that infectious diseases generally 
begin in rats, as they do for the most part in human beings, in young life, 
and by the time the rat has developed immune bodies and the spirochaetes 
are only limited to the kidney, it will not be more than half grown. Anyhow, 
working on this theory, I was able to find Trypanosoma lewisi in all stages of 
development in six out of 100 young rats which I examined during June and 
July 1913, whilst in the more mature and fully grown rats only the fully 
developed stage of trypanosomes were found. 
MORPHOLOGY OF SPIROCHAETA ICTEROPL AEMORRH AG1AE 
FOUND IN RATS. 
The spirochaetes found in the emulsion made from the kidney of rats do 
not always show movement. In one case, although the organisms were fairly 
numerous and could be definitely recognised by their characteristic shape, 
there were no signs of any activity, possibly owing to the time that had elapsed 
after the death of the rat, some 18 to 20 hours, but more probably owing to 
changes in the kidney. In most cases the distinctive side-to-side movements, 
of one or both ends, the central portion remaining rigid, were clearly seen, 
but in no case did I see much movement from place to place. 
In the fresh unstained conditions the majority of the parasites showed 
little or no internal structure, but in many granules could be seen, whilst in 
a few the spirochaete looked like a row of beads slowly waving about. 
Stokes says: “ With dark ground illumination we have been disappointed 
although the apparatus we use—a Leitz stage and a small arc lamp—shows 
S. pallida very well. With dark ground illumination they are much less 
retractile than S. pallida or S. refringensT This has not been my experience, 
I see these spirochaetes more readily than S. pallida. 
In the Giemsa stained preparations the rat spirochaetes stain a reddish 
colour, and in size, shape, and particularly in the recurved fish-hook-like ends, 
they were morphologically identical with S. icterohaemorrhagiae met with in 
