These facts led M. Pasteur to make researches on the comparative action of temperature on the fecundity of the spores of the mucidines, and of the germs which exist suspended in the atmosphere.
The following is, in few words, the method followed by him: He passed a small portion of asbestos over the small heads of the moulds which he wished to study; he then placed this asbestos, covered with spores, in a small glass tube, which he introduced into a U-tube (Fig. 4) of larger diameter, in which the smaller tube could move freely; one of the extremities of the U-tube is joined by India-rubber to a metal tube in form of a T, with stopcocks. One of these cocks communicated with the air-pump, another with a red-hot platinum tube. The other extremity has an India-rubber tube which is connected with the flask into which the spores are to be introduced; this flask is hermetically sealed, and has been filled with calcined air, and suitable nutritious liquid previously raised to the boiling-point. Finally, the U-tube dips into a bath of oil, of common water, or saltwater, according to the temperature which we wish to attain. Between' the U-tube and that of platinum, there is a drying-tube with sulphuric pumice-stone. When all the apparatus which precedes the platinum tube has been tilled with calcined air, and the spores have been maintained at the desired temperature for a sufficient time, which may be varied at pleasure, the point of the flask is broken with a blow of a hammer, without unfastening the India-rubber connecting-pieces which attach the flask to the U-tube; then inclining to a proper angle this latter tube, when removed from its bath, the asbestos with its spores is slipped into the flask. The flask is then hermetically sealed, and is carried to the stove at 68° to 86° Fahr. The experiment with the dust from the air is also made in the same manner with asbestos.
Without any humidity, the fecundity of the spores of Penecillium glaucum is preserved up to 248° Fahr., and even a little above—257° Fahr. It is the same with the spores of the other common mucidines. At 266° Fahr., the power of developing or multiplying is destroyed in all of them. The limits are the same for the dust from the air.
In all these careful experiments, the most scrupulous precautions were taken to prevent the access of the slightest portion of common air. But, say the partisans of heterogenesis, if the smallest portion of common air develops organisms in any infusion whatever, it must necessarily be the case that, if these organisms are not spontaneously generated, there must be germs of a multitude of various productions in this portion of common air, however small it may be; and, if things were so, the ordinary air would be loaded with organic matter, which would form a thick mist in it.
M. Pasteur has shown that there is a great deal of exaggeration in the opinion that even the smallest quantity of air is sufficient to develop multitudes of organisms; that, on the contrary, there is not in the atmosphere a continuous cause of these so-called spontaneous gen-
