Chiat PEK VEE 
THE ACTION OF DIRECT SUNLIGHT ON THE COMMON F2CAL 
ORGANISMS. 
WE now proceed with a study of the effect of natural 
influences on the common lactose fermenting fecal organisms. 
These, as we have seen, form by far the greater proportion 
of what may be termed the “‘ coliform ’’ organisms in feces, 
and are, on account of their numerical importance, the variety 
that should first be searched for in making study of the pollu- 
tion of water. The results quoted in Chapter V show that 
there is really no doubt that the common intestinal organism 
is a true lactose fermenter, so in dealing with a sample of 
water, unless a very full analysis is done, a study of the lactose 
fermenters will probably give the analyst most information. 
We entirely agree with MacConkey’s statement that a lactose 
broth is preferable to a glucose broth for ordinary work. 
From 4 years study of ordinary lactose fermenting organ- 
isms, several very interesting points have been discovered ; 
the most important of these has been obtained by what we 
call sunlight experiments. A reference to this work has 
already been made in the earlier chapters, but it is now 
necessary to describe the method in use more fully. A mixture 
of a known quantity of faces (usually one gramme per litre) is 
made in water, the grosser particles are filtered off with 
cotton-wool and the emulsion is placed in a flat dish in the 
sun, sometimes adding a layer of sterile sand at the bottom 
of the dishin order to make the experiment somewhat more 
natural. Samples of this emulsion are taken and carefully 
analysed at various intervals in order to see what alterations 
in the bacterial flora have taken place. Upwards of 50 of 
these experiments have been carried out during the course of 
our work, and we find that within broad lines certain varieties 
of lactose fermenting organisms disappear with much greater 
rapidity than do the others; that is to say, we find that there 
are some varieties which are very susceptible to the action 
