66 
cultured, gives a fair estimate of the organisms present in 
any sample, the actual number of organisms present is 
an important factor. In the emulsion of feces used by us, 
at the beginning of these experiments there were from 1,000 
to 10,000 fecal organisms per c.c. Obviously Io colonies 
selected from the organisms in 20 c.c. of this emulsion, can 
only give the organisms which preponderate numerically, 
the chances of isolating rare organisms being very small. 
But when the action of the sun has reduced the number of 
organisms from 10,000 per c.c. to I0—I00 per c.c., then it 
is reasonably certain that our methods of analysis give 
results which actually represent the flora of the emulsion at 
the time. 
On the other hand, when the organisms have been reduced 
to one in 50, or one in 100 c.c., another error has to be reckoned 
with; in the unfiltered emulsions it is common to get 
small particles of fecal matter, surrounded with an envelope 
of mucus, which may contain 3 or 4 different organisms that 
have, in this way, escaped the action of the rays of the sun. 
Examples of this accident have occurred in our experiments. 
Applying these remarks to the sunlight experiments, it is 
obvious that the early analyses on each case are approximate 
only, whilst the later ones (in so far as they are free from the 
second of these errors) are of very considerable value, and 
give a more correct estimate of the organisms present. 
Let us now say something about the various experiments 
commencing with No. 1. Unfortunately we have never 
again succeeded in getting such an instructive sample of 
human feces or cowdung as this one proved to be; the results 
are very striking. It will be noted that the sample originally 
contained bacillus coli communis in such numbers as to pre- 
ponderate over all the others in the original analysis. The 
emulsion was placed in the sun about noon of the 2nd Sep- 
tember and by the end of the 3rd, that is to say, presumably 
after about 18 hours’ exposure to sunlight, all the coli com- 
munis had disappeared, and were never found in the emulsion 
again. These coli being killed off, an entirely new set of 
organisms appeared in the analysis, namely, coscoroba, 
neapolitanus, pneumonize and Nos. 100 and 101. By the 
