[9]. The tube which conveys the debris of the body, together with the nutritious part of the food,—both measures of change or waste.
The results of the highly interesting experiments recently made by Professor Graham on the part taken by the active agent in all these processes—organic membrane, of which the organic cell is the type, demonstrates that all the phenomena known as Endosmose and Exosmose depend on a chemical action involving the destruction of organic membrane. In this process chemical action is set up dependent upon active chemical agents, neutral substances being inoperative. Out of this chemical action a new force is induced, the Osmotic force; a purely chemical being converted into an equivalent mechanical force, which is made subservient to the essential phenomena of organic and animal life: a vis motrix, a force which is to the extra-vascular movements of the body, what the contraction of the heart is to the vascular.
In a frame so constructed, any particles contaminating the circulating fluid most rapidly pervade and contaminate every part of the system.
It has been sometimes imagined that the quantity of matter suspended in the atmosphere and conveyed into the system in respired air, must be too minute to exert any serious influence upon the body.
One single puncture of the finger, so small as not to be visible without the aid of a lens, has introduced into the system a sufficient quantity of putrid matter to cause death with the most violent symptoms.
A few drops of the liquid matter obtained by a condensation of the air of a foul locality, introduced into the vein of a dog, is stated to have produced death with the usual phenomena of typhus fever.
It is certain that on the introduction into the body of an inappreciable portion of the matter of cow-pox, or of small-pox, those specific forms of fever are produced.
From these and similar facts it is inferred, that when putrescent or decomposing organic matter is introduced into the blood it acts as a poison and produces the phenomena of fever, and that all the predisposing causes of epidemics act in this way—by overcharging the blood with the products of decomposing organic matter.
Strictly speaking, however, all that we really know is this—that where certain conditions exist, epidemics break out and spread; that where those conditions do not exist, epidemics do not break out and spread; and that where those conditions did exist, but have been removed, thereupon epidemics cease.
We call those conditions Causes, Predisposing or Localizing Causes, but how they act, whether by accumulating decomposing organic matter in the blood, or in what other way, we have no certain knowledge.