What has been hitherto said, also applies to the more recent statements concerning the efficacy of cotton-wool as an agent for filtering germs from the atmosphere. Prof. Huxley says he has never seen putrefaction or fermentation occur after certain organic fluids have been boiled for ten or fifteen minutes, if a good plug of cotton-wool has been inserted into the neck of the flask in which they are contained whilst ebullition is going on, and has, subsequently, been allowed to remain in the same situation. Using other or perhaps stronger fluids, however, I have found that such a method of proceeding is by no means adequate to stop the growth and development of organisms. And, also, even if it had been always efficacious--the reason adduced could not hold good, in the face of my other experiments, which had shown that a development of life might go on in cases where the air, which had been similarly driven out, was subsequently, in place of being filtered, prevented from gaining access to the fluid. If germs derived from the air are the sole causes of putrefaction, then, surely, deprivation from air ought to be just as efficacious as any process of filtration of air--more especially when the filtration or the deprivation have a common starting point. And the mode of procedure, in both cases, is precisely the same up to a certain point. A fluid is boiled for a short time in order to kill the germs which may be within the flask, and to expel its previously contained air. At a certain stage of the ebullition, this may be arrested, if we have to do with a bent-neck flask, or one whose neck is plugged with cotton-wool, and no change, it is said, will subsequently take place in the contained fluid, because the air which enters is, by either of these means, filtered from its germs. But if, whilst ebullition continued, the neck of the flask had been hermetically sealed--so as altogether to prevent the re-ingress of air--and if the fluid, thus contained _in vacuo_, would nevertheless undergo fermentation, obviously the former explanation must be altogether shelved. In the face of M. Pasteur’s explanations, and those of Professor Huxley, these frequent positive results with fluids contained _in vacuo_ are absolutely contradictory. There may naturally arise, therefore, a very grave doubt as to the validity of the explanation adduced by M. Pasteur, and adopted by Professor Huxley and others. All these experiments to which I have been alluding are based upon the supposition (assented to by Pasteur and Huxley) that _Bacteria_ which pre-existed in the solution would certainly be destroyed by its being raised for a few minutes to a temperature of 212° F. This conclusion is, I believe, perfectly correct,[26] and in support thereof I will adduce the following additional information.