I). L. Mackinnon 
275 
temperature of 37° C., and I found it more convenient to use the 
serum only of citrated blood 1 . 
For the first half hour or so after being put into the warm stage, 
the spirochaetes were so active that it was impossible to follow any one 
individual. Gradually they slowed down somewhat, and it was at this 
stage that I made my observations. Later on, when they became still 
more sluggish, agglutination produced appearances often deceptively 
like divisions, which had to be discounted. Even when it was not a 
question of actual agglutination, the tendency of the spirochaetes to 
twist together for a short time in groups of two or three, made it very 
difficult to keep any one separately in view. At first also I lost many 
among blood-corpuscles. 
I. Longitudinal Division. On two occasions only did I see what 
I felt convinced were spirochaetes in process of longitudinal division. 
(1) The first was an individual that caught my attention by the 
character of its movement, which was slower and more spasmodic than 
that of the other spirochaetes in the same field. I then saw that it was 
apparently splitting longitudinally, and had already reached the Y-stage. 
The splitting portions were connected through the first two curves of 
their length, and then diverged at an acute angle : one individual had 
about seven curves free, the other was rather shorter. A certain amount 
of independent movement was shown in the two halves, one moving 
more rapidly or more slowly than the other; frequently they lay 
parallel, and twisted round one another, their curves coinciding or 
opposite. During the first fifteen minutes the spirochaete showed 
scarcely any appreciable forward movement, then it moved across the 
field, unsplit end first. Shortly before it was finally lost to sight—after 
having been watched for nearly 40 minutes—the split appeared to have 
extended over another curve. (Fig. 1 a, b, c, d .) 
(2) An individual, apparently in an advanced Y-stage of longi¬ 
tudinal division, was kept in sight for seven minutes. The two halves 
1 A simple method of obtaining small quantities of serum full of spirochaetes but almost 
free of blood corpuscles, is the following:—Draw up into a fine pipette, icith an opening 
narrower than the general lumen of the tube , a few drops of citrated blood. Lay the pipette 
horizontal for a short time; the blood corpuscles will settle in a layer in the under half of 
the lumen of the tube below the level of the opening, while numerous spirochaetes remain 
in the clear serum above. Then, still keeping the pipette nearly horizontal, blow out a 
minute drop of the serum on to a slide. This method has the advantage of avoiding 
possible injury to the organisms through centrifugalizing, and makes it easy to employ 
very small quantities of blood at a time. 
