63
drawn from the whole experiment would not be altered very materially, viz., that
the majority of A was more susceptible to the influence of the sun than the majority
of B and C. If however two very extreme cases were taken, such as a very delicate
organism and a very resistant one, it is highly probable that all the delicate organisms
would have disappeared before any great number of the very resistant ones had
.succumbed to the action of the sun.
It may be objected that, if we intend to formulate any law as to the viability of
bacilli, this law must obviously apply to all specimens of the same variety, in what-
ever situation they may be found in nature, otherwise the statement is of no value
in itself. We have no intention of doing anything so unwise as to lay down any
We
.and fast rules, for our experience teaches us that such do not exist in nature. We are
quite content with the very widest generalization, provided these are based on
observations from nature, and on the results of experiments carried. out as nearly as
possible under natural conditions. Imperfect as these experiments are, they are
amply sufficient to prove the correctness of certain wide conclusions.
Even if we have only succeeded in showing, that there does exist in fœcal matter,
any single organism, or group of organisms, that is distinctly more susceptible to the
action of the sunlight than any other, that single fact alone is worth a great deal to
sanitarian, who has to judge the purity of the water by his knowledgefœcal
fœcal of the natural
characteristics of the bacteria present in it. For if these susceptible organisms be
present in any water that has had some exposure to the sun, it is certain he is dealing
with a recent, and therefore dangerous contamination. On the other hand, the absence
of such organisms tends to show that, whatever the pollution may have been, the
chances of the water giving rise to epidemic disease are lessened.
We do not consider it necessary to say more about the individual experiments,
as the salient points in each have been noted. We would however draw particular
attention to the very striking results obtained in Experiment No. 1 (these have been
.already commented on) and to those of Experiments Nos: 20, 31, 33 and 34.
There is another point that requires discussion. Attention is particularly
• drawn to experiments Nos. 27, 28 and 32. To take No. 32 as the type, on the
emulsion being put into the sun 9 grunthal and 1 coscoroba were present. One hour
afterwards the analysis reveals an entirely different state of affairs. Only 2 grunthal
persist, coli communis arid sundry other organisms have made their appearance.
If a large number of grunthal had not disappeared during the first hour, they would
have still predominated in the second, third and fourth analyses to the exclusion of
other varieties. Consequently it is certain that quite a fair percentage of this bacillus
grunthal disappeared within the first hour. But as the experiment proceeds the usual
state of affairs declares itself, namely, cloacæ begins slowly to predominate and con--
tinues to do so up to within the last two analyses, when bacillus grunthal again comes
to the front and in the final analysis not a single other organism could be isolated.
It should be observed that this emulsion was made from five different specimens of
human fœces, and a layer of sand was placed at the bottom of the dish. Thus we are
absolutely forced to the conclusion, that, although a large number of the organisms,
included in the term bacillus grunthal, were sufficiently susceptible to die off in one
hour's exposure, the remainder were very resistant. Now it may be argued, that,
considering bacillus grunthal was by far the most numerous organism present at the
beginning of the experiment, the following explanation would completely satisfy all
the facts observed. Let it be granted that in a large number of individual bacilli
of the same species resistant and delicate specimens exist, then any organism that
preponderates at the beginning of the experiment will survive to the end, because the
mo:e organisms there are at the commencement, the greater is the chance of resistant
ones being included amongst the number of those experimented on. It must be admitted
that such explanation would account for all the results in Experiments Nos. 27, 28 and
32. But if this rule be applied universally, the results obtained would not be as
uniform as they are. Further, other experiments disprove this theory.
Thus in the
case of bacillus grunthal ; in Experiments Nos. 16, 17,19, 29 and 34 note the steady
increase in the number from beginning to end. In Experiment No. 20 note not a single
grunthal was isolated in the first analysis ; yet it survived all others. In Experiment
No 23 we find that the grunthals were fairly numerous at the beginning, they kept
-their 'numbers fairly even during the first four analyses, but died out altogether before