Observations on the Optical Deportment of the Atmosphere in Reference to the Phenomena of Putrefaction and Infection
Authors: J. Tyndall
Journal: BMJ (1876)

I. INTRODUCTION.-Theauthor alluded, in an introduction, to an inquiry on the decomposition of vapours, and the formation of actinic clouds, by l:ght, whereby he was led to experiments on the floating matter of the air.He refers to the experiments of Schwann, Schroeder and Dusch, Schroeder himself, to those of the illustrious French chemist Pasteur, to the reasoning of Lister and its experimental demonstration regarding the filtering power of the lungs; from all of which he concluded, six years ago, that the power of developing life by the air and its power of scattering light would be found to go hand in hand.He thought that the simple expedient of examining by means of a beam of light, while the eye was kept sensitive by darkness, the character of the medium in which their experiments were conducted, could not fail to be useful to workers in this field.But the method had not been much turned to account, and this year he thought it worth while to devote some time to the more complete demonstration of its utility.He also wished to free his mind, and if possible the minds of others, from the uncertainty and confusion which now beset the doctrine of " spontaneous generation".Pasteur has pronounced it "a chimera", and expressed the undoubting conviction that, this being so, it is possible to remove parasitic diseases from the earth.To the medical profession, therefore, and through them to humanity at large, this question is one of the last importance.But the state of medical opinion regarding it is not satisfactory.In a recent number of the BRITISH MEDICAL JOURNAL, and in answer to the question, " In what way is contagium generated and communicated ?"Messrs. Braidwood and Vacher reply that, notwithstanding " an almost incalculable amount of patient labour, the actual results obtained, especially as regards the manner of generation of contagium, have been most disappointing.Observers are even yet at variance whether these minute particles, whose dis- covery we have just noticed, and other disease germs, are always produced from like bodies previously existing, or whether they do not, under certain favourable conditions, spring into existence de nzovo." With a view to the possible dinminution of the uncertainty thus de.scribed, he submitted vithout further preface to the Royal Society, and especially to those wbo study the etiology of disease, a description of the mode of procedure followed in this inquiry, and of the results to which it had led.A number of chambers or cases were constructed, each with a glass front, its top, bottom, back, and sides being of wood.At the back is a little door, which opens and closes on hinges, while into the sides are inserted two panes of glass, facing each other.The top is perforated in the middle by a hole two inches in diameter, closed air-tight by a sheet of India-rubber.This sheet is pierced in the middle by a pin, and through the pin-hole is passed the shank of a long pipette ending above in a small funnel.A circular tin collar, two inches in diameter, and one inch and a half high, surrounds the pipette, the space between both being packed with cotton-wool moistened by glycerine.Thus, the pipette, in moving up and down, is not only firmly clasped by the India-rubber, but it also passes through a stuffing- box of sticky cotton-wool.The width of the aperture closed by the Tin-a-rub ber secures the free lateral play of the lower end of the pipette.Into two other smaller apertures in the top of the case are in- serted, air-tight, the open ends of two narrow tubes, intended to con- nect the interior space with the atmosphere.The tubes are bent several times up and down, so as to intercept and retain the particles carried by such feeble currents as changes of temperature might cause to set in between the outer and the inner air.