The main purpose for bringing these enormous quantities of air and blood together, with such velocity, is to provide for the enormous waste which is caused by the rapid and unceasing mutation of organic matter. The activity of an organ is sustained at the expense of the matter of which it is composed. No thought passes through the mind, but an equivalent portion of the substance of the brain is consumed; no nervous current flows along the nervous conducters, but a corresponding portion of nervous tissue is used up; no muscular movement, no glandular secretion, takes place without a proportionate waste of muscle and of gland. What must be the amount of supply required to meet this waste, when able-bodied men employed in their ordinary labour lose from 2 lbs. to 5 lbs. and upwards of their weight twice a day.[8] Some physiologists of eminence have estimated that in order to supply that waste, there passes in the course of every 24 hours as much fluid through the thoracic duct[9] as equals the whole quantity of blood in the body. Footnote 8: See Experiments on the daily loss of weight sustained by workmen employed in gas-works.—_Philosophy of Health_, 11th Edit. p. 284, _et seq._ Footnote 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.