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Scientific Memoirs by

     To a consideration of the practical measures thus indicated, a subsequent part
of this paper will be devoted. The whole tendency of the evidence adduced is to
incriminate the soil as the chief source of enteric fever and other bowel-complaints,
directly or indirectly, through the water and food supplies. A specifically polluted
soil is a constant source of danger to the inhabitants; a non-specifically polluted
soil is only one degree less dangerous as it provides a favorable medium for the
specific virus, and by its action on the individual it lowers the natural resistance to
that virus. The problem of removal and disposal involves above all thing an
avoidance of the pollution of the soil of the environment, at least so far as this
can reasonably be held to enter into direct relations with the community dwelling
thereon. It is necessary therefore, as a preliminary to the practical suggestions to
be made, to invite attention to the natural forces upon which we depend for the ulti-
mate mineralization of all waste organic matter, to the consideration of which the
writer was naturally led in the course of a series of experiments on the treatment
of the sewage of a large Indian community.

II.

     One of the very first uses to which the first microscope was applied was the
discovery by van Leeuwenhoek of minute living forms in the intestinal canals
of frogs and birds, and in his own diarrhœal evacuations. This was a purely objec-
tive observation, the significance of which only ripened slowly during the next two
hundred years; now we know that the richest hot-bed of bacteria in the animal
body is the intestine. With its alkalinity and its high and constant temperature,
putrefactive and fermentative organisms of all kinds, both aërobic and anaërobic,
find optimal conditions of existence. Escherich*has shown that in the interior
of the intestine, towards the centre of the mass that fills it, only anaërobic pro-
cesses can go on, but along the course of the walls in contact with the blood
vessels, aerobic changes can and do occur. According to the nature of the food
ingested we have a predominance of either putrefactive or fermentative changes
already set up in the alimentary canal, the first stages of those complex processes
of resolution to the ultimate forms in which Nitrogen and Carbon can re-enter the
cycle of life. The intestinal canal of the fœtus is sterile, but with the first food,
bacteria are conveyed to the intestine, an adaptation in small part to certain process-
es preparatory to assimilation, but chiefly to the ultimate resolution of the waste
products. But before we come to speak of bacterial action as specially directed

* " Die Darmbakterien."