(3-4 Royal Society: — Prof. J. Tyndall on the 



whereby he was led to experiment on the floating matter of the 

 air. lie refers to the experiments of Schwann, Schroder, and 

 Dusch, Schroder himself, to those of the illustrious French chemist 

 Pasteur, to the reasoning of Lister and its experimental verifi- 

 cation 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 the simple expedient of examin- 

 ing by means of a beam of light, while the eye was kept sensitive 

 by darkness, the character of the medium in which their experi- 

 ments were conducted could not fail to be useful to workers 

 in this field. But the method has 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 washed 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 huma- 

 nity 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 com- 

 municated ? " Messrs. Braidwood and Vacher reply that, notwith- 

 standing "an almost incalculable amount of patient labour, the 

 actual results obtained, especially as regards the manner of gene- 

 ration of contagium, have been most disappointing. Observers are 

 even yet at variance whether these minute particles, whose discovery 

 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 novo" 



With a view to the possible diminution of the uncertainty thus 

 described, the author submits without further preface to the Royal 

 Society, and especially to those who study the setiology of disease, 

 a description of the mode of procedure followed in this inquiry 

 and the results to which it has led. 



A number of chambers, or cases, were constructed, each with a 

 glass front, its top, bottom, back, and sides being of w T ood. 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 2 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, 2 inches in diameter and 1| inch 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 



