microscopic fungus, the achorion shoenleinii. It has been carefully studied by M. Bazin, a physician of the St. Louis hospital, who had long admitted the possibility of its transmission through the air, and who joined M. Lemaire in proving it. A youth of sixteen years, who had never received treatment, and who was afflicted with the disease in a severe form, was placed in a current of air, and at some distance a cooled vessel, from which the water of condensation was gathered; it was filled with living spores of the achorion, which had been conveyed by the air.

It is difficult to escape the conclusion derived from such skillful experiments, especially when we add others of M. Pasteur. He prepared a number of globes, the necks of which, drawn into long narrow tubes, were bent back and forth several times, and terminated in very small openings. He introduced into them albuminous sugared water, urine, or milk, which had been boiled some minutes, and left them, without closing, in a still place. Ebullition had destroyed all the moist germs the liquids had contained; the air which entered first, being hot, contained nothing living, and that which came in afterward, in its tardy progress, would deposit in the sinuosities of the tube the floating dust, which could scarcely reach the liquid; but the air would be continually renewed by variations of temperature and pressure, and the solution would eventu ally be in contact with air which had suffered no preparation, except being deprived of its dust. According to heterogeneity the globes would all be fruitful; according to panspermy, many would continue sterile. The experiment sustained panspermy.

We come now to another proof, the most simple of all, which still more clearly answers the objections of heterogeneity. M. Pasteur dispensed with long tortuous necks, but continued to use the same globes, ending in slender points, and the same scalded liquids. When all the air had been swept out by vapor, he closed the globes by melting the points. Air being thus excluded, the liquids were preserved indefinitely without mould or infusorial life, or change of any kind. At a given time the globes were opened and shortly sealed again, having received and brought in contact with the putrescible liquid a limited volume of air with all that it contained, and all its properties, known and unknown. The heterogenist

would here find all the conditions necessary for spontaneous generation, and might predict that each liquid would be peopled with all the species which would be developed if it were left in free air. The panspermatist would reason: In introducing air into the globe, there were introduced at the same time all the germs which it contained. But certainly so small a volume could not at once contain the spores and eggs of all known mucidines and infusoria, and since those it does contain are of different species, there will necessarily be considerable difference in the results if the experiment is frequently repeated. If to-day we introduce the spores of the penicilium glaucum, to-morrow this fungus will appear on the surface of the liquid. In another globe we may have eggs of colpods, in another of bacteria, and in general the same solution will be peopled with different beings in the different vessels. It may even happen that air not containing germs will have entered some of the globes, and in that case they will continue sterile, though all the conditions demanded by heterogeneity are realized. Such barrenness would occur quite often in caves, places where the air is still, in winter, or after a rain. It would be more rare in summer, in time of drought, and where the air abounds in germs. These are natural consequences of the principles of panspermy. Experience confirms this reasoning with mathematical precision."

M. Pasteur employed sixty similar globes containing the same solution. These he divided as they came into three series of twenty each. He then opened them in three different places chosen beforehand; the first series in the plain at the foot of Mt. Jura, the second on the high plateau of that range, the third at Montanvert, in the Mer de Glace, at the foot of the snows of Mont Blanc. Evidently the number of germs in the air of these localities should diminish as the elevation increases, in measure as it is removed from the meadows, fields, and waters whence they originate. Eight globes proved fertile in the plain; only five on the plateau of Jura; and of the twenty opened at Montanvert, one only developed mucidines. Thus it is shown that ordinary air does not always develop life in solutions, and that when it is divided into small separate volumes, some are fruitful and others are not. If heterogeneity is true, they should always be fruitful.

At this point occurred an episode, concerning which we cannot be silent, since it has its teaching. Messrs. Joly, Musset, and Pouchet had taken globes, prepared as those used by M. Pasteur, to the summit of the Pyrenees. Having opened them and filled them with air at La Rencluse and la Maladetta, they had seen organisms produced in all of them. These results, opposed to those obtained by M. Pasteur, but agreeing with the provisions of heterogeneity, established a discrepancy of fact between the observers. Every one saw the dawn of a hope of terminating the dispute by a decisive experiment. M. Pasteur gladly seized the occasion, and it was agreed to refer the question to the judges of the Academy, who named a commission of physiologists and chemists. The question was well put. "I affirm," said M. Pasteur, "that everywhere it is possible to detach a volume of air from the atmosphere which will contain neither egg nor spore, and will not produce generation in putrescible solutions." M. Joly wrote: "If one of our vessels continues unchanged, we will acknowledge our defeat." M. Pouchet still more explicitly added: "I assert that wherever I take a cubic decimetre of air, when I put it in contact with a fermentible liquid in a close vessel, it will give birth to living organisms." The parties thus engaging with a certain solemnity, the issue seemed closed. This was in January, 1864. Some time afterward the heterogenists asked that the experiment might be delayed till the season of hot weather. M. Pasteur, with some regret, consented to the delay, and it was not until the 15th of June that the commission and the champions could be got together. The commission, in view of the origin of the debate, wished to restrict it to the single experiment which had provoked it, and ought to end it, since it bore upon a single fact. The heterogenists would not admit this, and undertook to repeat their long series of experiments. This would be to reopen the discussion, and render the judgment as long as the dispute had been. The commission persisting, the heterogenists felt authorized to retire. It is perhaps unfortunate that the commission adhered so strictly to the programme on this occasion. But it is evident that the heterogenists, however they may have colored their retreat, are selfcondemned. If they had been sure of the fact which they had solemnly engaged to prove or acknowledge themselves con

quered, they would have persisted in demonstrating it, for it would have been the triumph of their doctrine. Only causes not sure are allowed to go by default.

When discussions of so high a degree of scientific interest claim the attention of the public, it seems the duty of masters to put in the balance the weight of their authority. Thus it is with pleasure that we have seen M. Coste, the eminent embryologist, assert the right to correct interpretations which he deems erroneous. From the very first he has transferred the question to a new ground, by withdrawing it from the range of general experiments and philosophical reasoning, and subjecting it to the test of the observation of each microscopic species at the moment of its birth, development, and multiplication, to generalize afterward with surety upon the particular facts. M. Coste selected the colpods, which are quite large and easy to observe and follow. They are sure to be found in a maceration of hay. Any one can observe them and study their motions and habits with a small microscope. By the aid of their vibrating cilia they move rapidly in every direction, avoid or meet each other, appear in continual quest, and often gather in close groups on the masses of monads or vibrions on which they prey. When. they are well fed and large they may be seen to stop, turn upon themselves, and secrete at the expense of their substance a spherical membrane which envelopes them, shuts them up, and in which they are encased in complete immobility, as a chrysalis in its cocoon. In this cyst there shortly appear separations more and more marked, dividing the mass into four, eight, or even twelve chambers, each habited by a little colpod, which gradually unfolds itself, and soon the whole nest escapes, one at a time, through a hole in the envelope. They may then be seen to grow, and some hours afterward recommence, each on its own account, the evolutions to which they owe their common birth. This process of reproduction is called the encystment of multiplication. The colpods have also at their disposition another method, discovered by M. Gerbe. Two old colpods which had already gone through the process of subdivision, thin and transparent, sought each other, and joining by the ventral portions, clung together as one. In this condition they formed a common cyst, and preserved for some time an absolute immobility, during which progressive interior

changes might be witnessed. At length four roundish bodies, four eggs, escaped from the envelop. The parents disappeared, but the eggs gradually took the form of little colpods. Ehrenberg, an authority in these matters, speaks of a third mode of generation. He has surprised and figured a colpod in the act of emitting a multitude of extremely small eggs. Thus we see what a multiplicity of different processes, equally fruitful, nature has provided for the multiplication of these singular animals. She also gives them the faculty of suspending life when they are dry, and of resuming it when they are moistened. In 1857, M. Balbiani observed a drop of water on a plate of glass in which were living colpods. When the water evaporated each became encysted and dormant in its envelope. The plate was moistened again in 1864, when every colpod was observed to come out from its shell and resume its vital functions, which had been interrupted by seven years of sleep. Thus colpods live in pools, are encysted when these dry, and revive as soon as water is restored. They live and multiply when it rains on leaves, meadows, in crevices of rock and furrows of earth, and in dry weather escape dormant in the dust, to carry everywhere the fruitful seeds of their species.

It remains to be told how the colpods come, and how M. Coste explains their pretended spontaneous generation. He shook a handful of hay over a sheet of paper. He collected the dust which fell, placed it in water and watched it. He soon discovered the cysts of colpods, and keeping his eyes upon them, saw them shortly revive, and begin to move. These had been on the hay, since there were found in its dust cysts of colpods dried and preserved. It has been established that they will revive when moistened; but they do not produce themselves. There is a reawakening, not a birth; a return to active life after lethargy, and not a spontaneous generation. The result is the same when, instead of shaking off the dust, the hay is macerated in water. The cysts on the leaves float off, and this is the way that inattentive observers imagine that the colpods whose cysts they have not seen are spontaneously engendered by the maceration. The liquid may be filtered without changing the result. M. Coste has proved that filters, even when placed one upon another, give passage to colpods and their eggs, to bacteria, vibrions, and monads. However few may have passed,