104 MICRO-ORGANISMS IN RELATION TO MAN. 
may be so grouped that they form long wavy or spiral threads, 
each of which may be made up of 10, 20, or even 30 short 
turns. 
If plate-cultures of this bacillus, made according to Koch’s 
method, be kept in a chamber in which the temperature is 
maintained at a little over 68° F., small greyish or white 
points are first seen; examined with a low-power lens, each 
of these is seen to have a slight yellow tinge and a somewhat 
wavy margin; as the colony increases in size its colour be- 
comes slightly deeper, the margin becomes more and more 
crenated and the surface somewhat granular. Slow lique- 
faction of the gelatine is now found to take place, and small 
funnel-shaped depressions are seen in the gelatine. The 
liquefaction increases with the age of the culture, and 
towards the sixth day the colony has sometimes a delicate 
pink tinge—a most characteristic feature when present. 
Another distinctive feature of the cholera bacillus is the 
puncture culture in gelatine. This consists in dipping a 
sterilised needle in a culture of the bacillus and then plunging 
it into sterilised gelatine contained in a test-tube. Cells of 
the organism are left along the track of the needle, and the 
growth under these circumstances is very characteristic. It 
takes place along the whole track of the needle, first as a 
delicate white cloud, then, gradually becoming more and more 
marked, it forms a delicate streak, around which there is 
usually a clear space, due to the liquefaction of the gelatine 
along the track of the needle. Near the surface, the lique- 
faction goes on more rapidly than deeper down, and at the 
end of forty-eight hours there is a distinct funnel-shaped area. 
About the fourth day of growth, this funnel is still more 
marked, but the upper portion has become quite clear, the 
central thread having fallen to the lower and narrower part 
of the funnel, where it may be seen as a comparatively 
short spiral, the thread as it sinks being arranged in regular 
bights, like those of a cable. 
