9
according to their reaction in certain sugars. Considering that we know so little
about the bacteriology of the waters of this country, and considering also that there
is very little doubt that very material differences exist between the bacteriological
flora found in the tropics and in cold climates, it is obvious that the more information
we obtain, the better we shall be able to formulate working standards. Indeed we
consider that it is necessary to begin at the very beginning in this research, and in
order to do so it is important to separate individual bacilli and. not sub-divide them into
certain arbitrary groups. Of course it may be argued that the method is much too
long, complicated and expensive to be used in the laboratory where large number of
samples have to be worked through. We are prepared to admit the truth of this
statement up to a certain point ; in the future, when we have accumulated sufficient
data to justify us in formulating certain broad rules, it may be possible to shorten the
method to a considerable extent ; but until such time it is necessary to go into detail
up. We do not propose to discuss the problem of the constancy of the reaction of
organisms in the various sugars ; for the purpose of this report, it is accepted that the
same species of bacilli always ferments the same sugar. If further information be
required, the discussion of this subject will be found in MacConkey's paper already
referred to (Journal of Hygiene, Vol. VI, No. 3, July 1906).
(4) Voges and Proskauer Reaction.— The Voges and Proskauer reaction has been
the subject of very considerable controversy. Some regard this test as being very
variable, at one time giving the reaction, and at another failing to give it with the same
bacillus. Orr in his work on milk says “ The reaction has been given by other
organisms than Lactis erogenes, B. Cloacæ, Oxytocus perniciosus more especially by
those of the proteus group. It is not given constantly by all bacilli of these groups,
although it is apparently a very constant and excellent confirmatory test for B. Cloacæ
and Oxytocus perniciosus. It is not apparently so good a test for B. Lactis ænrogenes
as stated by MacConkey.” This, however, has not been our experience with organisms
derived from water, fœces, earth, etc. The reaction appears to us to be a very satis-
factory test, if certain simple precautions, such as, adding a fair quantity of the culture
to the glucose broth, incubating for 48 hours or more, are always observed. Some
care has to be exercised, as in all similar reactions, for in some instances the
colour is rather faint. If, however, a very small quantity (2 or 3 drops) of a
saturated solution of caustic potash is used, instead of a large quantity of dilute solution,
the amount of fluid in the tube is not increased, and the colour very seldom fails to
appear in sufficient quantities to be easily recognisable in two hours.
(5)
Indol test .—MacConkey, in his recent work, has shown the necessity for
doing the indol test, making use of the new benzaldehyd method. Unfortunately
during two of the quarters described in this report, this test was not used, but it
should certainly form 'part of the regular routine. The formation of indol, is, like
Voges and Proskauer reaction, a test about which opinions differ somewhat, an
d c e r t a i n l y w i t h t h e o l d m e t h o d r e s u l t s w e r e n o t v e r y s a t i s f a c t o r y . T h e i n t r o d u c t i o n o f
the benzaldehyd method may remove this objection to a considerable degree.
(6) Motility.—On the subject of motility as a constant characteristic of any
organism opinion is again divided. Admitting, for the sake of argument, that motility
is a perfectly constant character of a given species of bacillus, in other words a motile
organism possesses cilia and a non-motile one does not, it nevertheless is certain that
ab a c t e r i u m t h a t i s r e a l l y m o t i l e , m a y b e f o u n d a t t i m e s w i t h l o s s o f m o t i l i t y w h i c h
can be easily restored to it by culturing it. If the work of this report had for its
object the solution of purely bacteriological problems, then all non-motile organisms
would be cultured two or three times in broth in order to ascertain if this characteristic
had been temporarily lost. But for routine work this is out of the question, conse-
quently we recommend that motility be carefully looked for once, viz., after 18 hours'
c u l t i v a t i o n i n b r o t h , b u t t h a t w h e n a n e g a t i v e r e s u l t i s o b t a i n e d t o o m u c h i m p o r t a n c e
b e n o t a t t a c h e d t o t h e r e s u l t , a s t h e r e c a n b e n o d o u b t t h a t t h i s t e s t i s n o t o f t h e
same
order of importance as the power to ferment a sugar or alcohol. We have some
e x p e r i m e n t s w h i c h t e n d t o s h o w t h a t a n o r g a n i s m l o s e s i t s p o w e r o f m o t i l i t y b y t h e
a c t i o n
of the sun and does not recover it easily by the growth in the media
e n u m e r a t e d a b o v e .
NOTE.— Much seems to depend on the medium not being too acid, or rather being sufficiently alkaline.
3