246 THE MICROSCOPICAL NEWS. 
. 
Minute plants play an important part in another way. The num- 
ber per gallon of suspended diatoms, desmids, and confervoid algz 
is, in some cases, most astonishing, and they must often produce 
much more effect than the larger plants. As far as I have been 
able to ascertain, their number is, to some extent, related to the 
amount of material suitable for their assimilation and growth. In 
the mud deposited from pure rivers their numbers is relatively 
small, but in the district of the Thames, where the sewage is dis- 
charged, I found that in summer their number per grain of mud at 
half-ebb tide was about 400,000, which is equivalent to above 
5,000,000 per gallon of water. ‘This is two or three times as many 
as higher up or lower down the river, and, out of all proportion, 
more than in the case of fairly pure rivers like the Medway. ‘Their 
effect in oxygenating the water must be very important, since, 
when exposed to the light, they would decompose carbonic acid, 
and give off oxygen, under circumstances most favourable for 
supplying the needs of animal life, and counteracting the putre- 
factive decomposition so soon set up by minute fungi when oxygen 
is absent. 
Taking then, all the above facts into consideration, it appears 
to me that the removal of impurities from rivers is more a biological 
than a chemical question; and that in all discussions of the 
subject it is most important to consider the action of minute 
animals and plants, which may be looked upon as being indirectly 
most powerful chemical reagents. 
REMARKS ON PATHOGENIC BACTERIA. 
By Dr. H. J. Detmers, F.R.MLS. 
(Continued from page 240.) 
Ae this, however, hardly affords a sufficient or satisfactory ex- 
planation as to the conditions necessary, on the one hand, to 
the exercise of the malignant properties of pathogenic bacteria, and 
on the other, to check the action of those malignant properties. I 
may here remark, I repeatedly found swine-plague micrococci, or, 
rather, diplococci, in the affected portions of the lungs and in the 
lymphatic glands of hogs that had recovered, or were recovering, 
from an attack of swine-plague. I found them four and five weeks 
after the morbid process had ceased to act, or, perhaps, more 
correctly, after a retrogressive process had set in.. Consequently, 
those micrococci had become dormant, or had ceased to do mischief, 
