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through obstacles intricate and close enough to arrest and retain them. To accomplish this, M. Pasteur passed several cubic meters of air through a narrow tube, into which he had previously introduced a long wad of amianthus or tow, or better still, gun-cotton. The wad was perceptibly soiled by the experiment; it was evident that the greater number, if not the whole, of the floating atoms had been deposited upon it. It was digested in a mixture of alcohol and ether, which has the property of dissolving gun-cotton; the dust fell to the bottom of the vessel, whence it was collected and studied under the microscope. Among the coarse fraginents and sediment were perceived a number of roundish organic bodies, which in volume and general aspect seemed identical with the spores of mucidines and eggs of infusoria which had already been recognized in microscopic observations of the dust which is naturally deposited on polished surfaces when left in the air.

Shortly afterward M. Pouchet made analogous researches by a different process. He contrived an instrument which he called an aeroscope, consisting essentially of a tube with a fine point, through which the air to be studied was passed in a jet, and received upon a plate of glass covered with some viscous substance. This jet deposited a pile of dust, which was subjected to the microscope. With this instrument M. Pouchet collected coal dust, inorganic debris, feathers, hairs, grains of starch, etc., but none or few of organic germs. He performed his experiments in different countries. According to M. Joly, “He examined the particles which find their way into the respiratory cavities of men and animals; the accumulated dust of centuries in the cathedrals; that of the air in public halls, theaters, and hospitals. He crossed seas, and ascended high mountains; he went into the tombs of the Pharaohs and examined their dusty and blackened skulls." Why were the researches of M. Pouchet so constantly negative, and those of M. Pasteur, who did not go so far, always fruitful? The difference in the results is not surprising. The success of the one is owing to his thorough process of investigation; the failure of the other to his aeroscope, which is worthless. A skillful experimentist, Dr. Sales-Girons, proposed to impregnate air with the impalpable precipitate of mineral waters for the breathing of the sick,

and to show that his medicaments would reach the bronchial vessels, he endeavored to pass them through sharply-curved tubes of glass moistened, so that the air charged with mineral particles should strike at each curve a wall of glass, as in M. Pouchet's aeroscope. He has conclusively shown that the coarse particles were arrested by these obstacles, while the fine ones passed on. So the aeroscope collected the gross particles from the atmosphere, but let pass the more minute spores and eggs. Thus M. Pouchet never found them, while M. Pasteur obtained them, saw them, and exhibited them. How could he have done this if they had not existed?

Strongly bearing against M. Pouchet are the recent remarkable studies of Dr. Lemaire and Professor Gratiolet, who have lately attempted with success the first serious physiological analysis of the atmosphere. By means of an instrument called an aspirator they slowly conducted air by a fine tube through water, in which it was washed, and left the floating bodies, great and small, which it contained. To this method, the efficacy and simplicity of which are evident, they add another yet more ingenious, which is within the reach of the least skillful. It is by placing at any required spot a saucer, in which stands a closed vase filled with ice. The moisture of the air condensing on the vase drops into the saucer, carrying with it the atmospheric dust which had come in contact with the vase. Wherever the analysis has been performed an abundant harvest of spores and infusorial germs has been obtained. They have been found in every kind of grain, in preserved food, and even in medical preparations.

Thus it can no longer be doubted that there are germs everywhere. It remains to be proved that whenever we take them away or kill them we at the same time destroy the fecundity of infusions. We had already the conclusive experiments of Schultze and Schwann upon this point, but without dwelling upon these we will merely relate how M. Pasteur has repeated them and improved upon them. He introduced into several similar globes an equal quantity of a putrescible solution which had been boiled for fifteen minutes. The ebullition produced the double effect of destroying by cooking all the germs which might have been in the liquid and in the globes, and of sweeping out the interior with a current of steam. While cooling,

ordinary atmospheric air, bringing with it the germs and the so-called spontaneous generation, was allowed to enter a part of the globes, while air in which the germs had been burnt by passing through a red-hot tube was introduced into the others. The latter were invariably sterile; the germs having been suppressed, all further life was destroyed.

Having thus shown the presence in floating dust of what seemed to be spores and eggs, and having proved that by heating air was rendered sterile, M. Pasteur had only to demonstrate that these were really fertile germs. To do this he had to plant them. Having prepared as before a barren solution by boiling it and keeping it in a vessel of air that had been scorched, he put into it a small tube containing a wad of amianthus. The solution continued sterile or fertile according to circumstances: always sterile when the wad had been heated red hot, and contained no germs; always fertile when it had previously been filtrated with air and had collected the roundish bodies upon its filaments. When the contact of atmospheric air was allowed, generation took place at the end of twenty-four or thirty hours, and always at the points on the amianthus where the germs had been placed. Thus the germs were collected, planted, and developed.

M. Pouchet repeated M. Pasteur's experiment, with the difference, that instead of tubes containing amianthus, he placed in the sterile vessel hay, leaves, or other putrescible substances which had been exposed for an hour and a half to a heat of 150° cent. (He adds in a note that the temperature might be increased to 200° cent.) There appeared sometimes after a protracted period mucidines, vibrions, and bacteria, but in no case ciliated infusoria. He explains this result by saying that if there had been germs in the putrescible matter they would have been decomposed by the high temperature to which they had been exposed, and that the fertility of the solution could in this case only be explained by heterogeneity. This argument would be incontrovertible if it was demonstrated that infusoria could not sustain great variations of temperature without destruction; but, as we shall see, this is not the case.

It was shown some time ago by M. Chevreuil that the white of an egg, heated to 100° cent., will be cooked, and become insoluble in water; but that if it is first dried when cool, and

then heated to 100° cent. for an hour and a half, it will not coagulate, and when cooled again may be dissolved in water and will resume the properties it had when fresh. Now the white of an egg is the albumen of the animal tissues and eggs. Although eggs are rendered sterile by heating till their albumen is coagulated, there seems to be no reason why their fertility should be destroyed by heat if coagulation does not take place. Observation fully justifies this reasoning. Spallanzi has found under the tiles of roofs rotiferæ, which may be heated to 100° cent. if dry, and will revive if placed in water. M. Doyer has made similar observations on other classes of animalcula with similar results. It is, then, not impossible that the spores of mucidines and the eggs of vibrions may survive a temperature of 100 cent. It is only a question of specific endurance. The difficulty, moreover, would seem as great for heterogeneity as for panspermy. Heterogeneity supposes in effect that the life of organic substances is transmitted to microscopic beings. It would be as difficult to believe that life could resist a temperature of 200° cent. in these conditions as to admit its preservation at this temperature in eggs or seeds.

But the heterogenists go further. They say to their adversaries: "You have introduced scorched air into a boiled solution, and have suppressed generation. Grant that you have burnt the germs which might have been in the air, are you sure that you have not at the same time destroyed some vivifying quality of the air, some unknown principle which may be the cause of spontaneous generations, some unanalyzed and unanalyzable kind of seminal air? Again, you plant the atmospheric bodies in amianthus, and say that it is they which have germinated. How do you know it? Has not the amianthus imbibed this vital principle of the air? Your experiment is no demonstration as long as these hypotheses are possible. To establish your conclusions you must show the same results without employing fire, acids, or any substance which can change the physiological properties of the air."

The panspermatists replied to these objections, which were not wanting in force, with new experiments. It will be remembered that the experiments of Messrs. Gratiolet and Lemaire consisted in collecting the germs of the air of the place of investigation in water, and examining the liquid under the

microscope. They began at Sologne, in a very unhealthy locality, on a pond in the neighborhood of a village which had a bad reputation for the prevalence of miasmatic fevers. The water had a marshy odor, and contained no living being. There appeared myriads of spherical, roundish, and fusiform spores, pale cells, and semi-transparent ovoid bodies. At the end of fifteen hours, a large number of these germs having been developed, upward of two hundred bacteria were found in a single drop. After forty-eight hours the water swarmed with vibrions and spirilla; and on the third day monads, whose incubation seemed slower, were moving in all directions. While this mass of beings was being thus developed, the germs from which they originated necessarily disappeared. There could be no question of spontaneous generation here, for they had to deal with pure water, which never produces infusoria. As the water could not support its population, they were forced to prey upon each other. The bacteria were first sacrificed, then the vibrions and spirilla disappeared, after which the monads eat each other up. After fifteen days the largest alone survived. Then the water became pure again, and might be kept an indefinite time without repeopling itself. It had then obtained its germs from the air. If organic matter had been added so that the infusoria could have obtained food, they would have multiplied as long as it lasted, and would have done each other no harm. The experiment was repeated in a region noted for its salubrity, at Romainville, ninety meters above the Seine, among cultivated fields. Similar germs were found there, and gave birth to the same species of infusoria; but being less numerous they disappeared in three days. Between these extremes different localities were examined and classed according to the abundance of their aerial germs. Air was also analyzed which had stood or been passed near macerations containing infusoria. Syrup in fermentation, filled with yeast, gave out spores of this plant which the air took away; and on washing a current which had passed over a maceration of tainted meat, germs were obtained, which were hatched in the water, and reproduced all the infusoria of the maceration.

To these remarkable examples we will add the following observation, the most curious of all. That terrible malady which attacks hairy skin, the favus, or scald-head, is produced by a

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