129 THE AMERICAN MONTHLY [December, 
ness of Dr. E. O. Shakespeare I was enabled to compare it with cultures of 
the three spirilla thus far discovered. By making cultures of all at the same 
time and exposing them to similar conditions of temperature, relative alka- 
linity, and concentration of culture media, accurate comparisons could be 
made. : 
The spirillum under consideration resembles the spirillum of Finkler and 
Prior so closely that it may be regarded as a slightly modified variety of this 
microbe. For the sake of brevity it will be denominated spirillum /, the 
original spirillum of Finkler and Prior spirillum «. The spirilla mentioned 
above have been very carefully described in many publications by writers on 
cholera, so that the reader will be spared any unnecessary repetitions.* 
In tubes and on plates, spirillum / liquefies the commonly used 10 per 
cent. gelatin mach more rapidly than spirillum «. At a temperature of 22° 
to 24° C. the plate containing colonies of the former was completely liquefied 
on the third day, that containing colonies of the latter only partially so. The 
coloniest of these two forms do not differ in any other way. Before lique- 
faction sets in, they present a homogeneous, circular disk with sharp, regular 
margin and a darker central nucleus which appears on the second day. 
In tubes spirillum / liquefies the gelatin twice as rapidly as spirillum 4 
during the first two or three days. Later on, both microbes seem to ex- 
perience the same difficulty in the downward liquefaction of the gelatin, and 
after the first week they look alike. 
On boiled potato spirillum « grew best at 20°-24°C. Spirillum # multiplied 
very slightly at this temperature. A feeble growth may appear at 35° C., 
which then resembles that of spirillum « in color and consistency. In gen- 
eral the latter grows far more vigorously on potato than the former. 
In liquid media such as simple beef infusion, or beef infusion containing 1 
per cent. peptone, both made slightly alkaline with sodium carbonate, the mul- 
tiplication of this organism and of the other spirilla deserves some attention. 
The employment of liquid media as an accessory means of distinguishing them 
from one another has not received any attention whatever, although it is of 
considerable value as the following shows :—If the spirilla of Koch, Finkler 
and Prior, and Deneke be added to beef infusion and the tubes placed in a 
temperature of about 35° C. the following changes may be seen after twenty- 
four hours. The tube inoculated with Koch’s spirillum will be clouded and 
the surface of the liquid covered with a delicate but complete membrane. 
Beneath this the upper strata will be quite turbid from the very abundant 
massing of spirilla. The infusion inoculated with the Finkler and Prior 
spirillum is barely opalescent, without any trace of a surface membrane. 
The third tube inoculated with the Deneke spirillum remains permanently 
clear. These differences have reappeared with each succeeding test, so that 
they may be regarded as constant; the same is true of beef infusion containing 
I per cent. peptone. 
That the spirillum of Koch has a tendency to rise to the surface in culture 
media and there form a membrane is not a new fact. It has been made use 
* Very good descriptions will be found in Fliigge (I. c.) < 
+ In studying these it is very important not only to know the concentration of the gelatin employed, but to 
keep it in as uniform a temperature as possible, since both of these conditions have a marked influence upon the 
characters of the colony in its development. It is exceedingly difficult to realize a uniform, low temperature, 
both in summer and winter. In summer, the temperature in this climate is above the melting point of 10 per 
cent. gelatin for weeks and months. In winter a thermo-regulator usually fails within the narrow limit be- 
tween the average temperature of the laboratory and that at which it is desirable to maintain the gelatin. A 
given per cent. of gelatin at a low temperature is equivalent to a larger per cent. at a higher temperature. The 
density, in other words, is increased when the temperature falls. We know, for instance, that the most impor- 
tant diagnostic feature of the cholera spirillum is the peculiar appearance ofits colonies on the gelatin plates— 
a certain irregularity of outline combined with a marked refrangibility as of ‘ particles of glass... The writer 
has, however, seen these very colonies present smooth, sharply outlined disks, differing from those of the other 
spirilla only in size. This loss of characteristic features was due to an abnormally low temperature at the time. 
A few days later, another plate growing in a higher temperature presented colonies of the usual type. 
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