Whilst this work was passing through the press there appeared two small works on the subject of the generation of inferior organisms.

One of them was by M. Fremy. The author’s object seems to have been merely to give an account, under a new form, of the part which he took in the discussion on the origin of ferments that was carried on before the Academy of Sciences in 1871-1872. In the course of that discussion M. Fremy had announced his intention of publishing an extensive Memoir, full of facts, bearing on the subject. The perusal of the promised work gave us much disappointment. Not only were our experiments, and the conclusions which we drew from them, given there, for the most part in a manner which we could not possibly accept, but, moreover, M. Fremy had confined himself to deducing, by the help of his favourite hypothesis, a series of À priori opinions based on half-finished experiments, not one of which, in our opinion, had been brought to the state of demonstration. To tell the truth, his work was the romance of hemi-organism, just as M. Pouchet’s work of an earlier date was the romance of heterogenesis. And yet, what could be clearer than the subject under discussion? We maintain, adducing incontestable experimental evidence in support of our theory, that living, organized ferments spring only from similar organisms likewise endowed with life; and that the germs of these ferments exist in a state of suspension in the air, or on the exterior surface of objects. M. Fremy asserts that these ferments are formed by the force of hemi-organism acting on albuminous substances, in contact with air. We may put the matter more precisely by two examples:—

Wine is produced by a ferment, that is to say, by minute, vegetative cells which multiply by budding. According to us, the germs of these cells abound in autumn on the surface of grapes and the woody parts of their bunches; and the proofs which we have given of this fact are as clear as any evidence can be. According to M. Fremy, the cells of ferment are produced by spontaneous generation, that is to say, by the transformation of nitrogenous substances contained in the juice of the grape, as soon as that juice is brought into contact with air.

Again, blood flows from a vein; it putrefies, and in a very short time swarms with bacteria or vibrios. According to us the germs of these bacteria and vibrios have been introduced by particles of dust floating in the air or derived from the surface of objects, possibly the body of the wounded animal, or the vessels employed, or a variety of other objects. M. Fremy, on the other hand, asserts that these bacteria or vibrios are produced spontaneously, because the albumen, and the fibrin of the blood themselves possess a semi-organization, which causes them, when in contact with air, to change spontaneously into these marvellously active minute beings.

Has M. Fremy given any proof of the truth of his theory? By no manner of means; he confines himself to asserting that things are as he says they are. He is constantly speaking of hemi-organism and its effects, but we do not find his affirmations supported by a single experimental proof. There is, nevertheless, a very simple means of testing the truth of the theory of hemi-organism; and on this point M. Fremy and ourselves are quite at one. This means consists in taking a quantity of grape juice, blood, wine, &c., from the very interior of the organs which contain those liquids, with the necessary precautions to avoid contact with the particles of dust in suspension in the air or spread over objects. According to the hypothesis of M. Fremy, these liquids must of necessity ferment in the presence of pure air. According to us, the very opposite of this must be the case. Here, then, is a crucial experiment of the most decisive kind for determining the merits of the rival theories, a criterion, moreover, which M. Fremy perfectly admits. In 1863, and again in 1872, we published the earliest experiments that were made in accordance with this decisive method. The result was as follows:—The grape juice did not ferment in vessels full of air, air deprived of its particles of dust—that is to say, it did not produce any of the ferments of wine; the blood did not putrefy—that is to say, it yielded neither bacteria nor vibrios; urine did not become ammoniacal—that is to say, it did not give rise to any organism; in a word the origin of life manifested itself in no single instance.

In the presence of arguments so irresistible as these, M. Fremy, throughout the 250 pages of his work, continues to repeat that these results, which, he admits, seem subversive of his theory, are, nevertheless, explicable by the circumstance that the air in our vessels, although pure at first, underwent a sudden chemical change when it came in contact with the blood, or urine, or grape juice; that the oxygen became converted into carbonic acid gas, and that, in consequence, hemi-organism could no longer exercise its force. We are astonished at this assertion, for M. Fremy must be aware that, since 1863, we have given analyses of the air in our vessels after they had remained sterile for several days—for ten, twenty, thirty, or forty days—at the highest atmospheric temperatures, and that oxygen was still present, often even in proportions almost identical with those to be found in atmospheric air.^[185] Why has M. Fremy made no allusion to these analyses? This was the chief, the essential point in question. Besides, if M. Fremy had wished to test the truth of his explanation, there was a very simple means of restoring the purity of the air in contact with the liquids open to him; he might have passed through his vessels a slow and continuous current of pure air, day and night. We have done this a hundred times, and we have always found that the sterility of the putrescible or fermentable liquids remained unaffected.

The hemi-organism hypothesis is, therefore, absolutely untenable, and we have no doubt that our learned friend will eventually declare as much before the Academy, since he has more than once publicly expressed his readiness to do so as soon as our demonstrations appear convincing to him. How can he resist the evidence of such facts and proofs? Persistence in such a course can benefit nobody, but it may depreciate the dignity of science in general esteem. It would gratify us extremely to find the rigorous exactness of our studies on this subject acknowledged by M. Fremy, and regarded by that gentleman with the same favour bestowed upon it everywhere abroad. It may be doubted if there exists at the present day a single person beyond the Rhine who believes in the correctness of Liebig’s theory, of which M. Fremy’s hemi-organism is merely a variation. If M. Fremy still hesitates to accept our demonstrations, the observations of Mr. Tyndall may effect his conversion.

The other publication to which we alluded was the work of the celebrated English physicist, John Tyndall. It was read before the Royal Society of London, at a meeting held on January 13, 1876.

The following letter explains how the illustrious successor of Faraday at the Royal Institution came to undertake these researches:—

“London, February 16, 1876.

“Dear Mr. Pasteur,—

“In the course of the last few years a number of works bearing such titles as ‘The Beginnings of Life’; ‘Evolution and the Origin of Life,’ &c., have been published in England by a young physician, Dr. Bastian. The same author has also published a considerable number of articles in different reviews and journals. The very circumstantial manner in which he describes his experiments, and the tone of assurance with which he advances his conclusions, have produced an immense impression on the English as well as the American public. But what is more serious still, from a practical point of view, is the influence that these writings have exercised on the medical world. He has attacked your works with great vigour, and, although he has made but slight impression on those who know them thoroughly, yet he has succeeded in producing a very great and, I may add, a very pernicious one on others.

“The state of confusion and uncertainty had come to be so great that, about six months ago, I thought that I should be rendering a service to science, and at the same time performing an act of justice to yourself, in submitting the question to a fresh investigation. Putting into execution an idea which I had entertained for some six years, the details of which were set forth in an article in the British Medical Journal, which I had the pleasure of sending you, I have gone over a great deal of the ground on which Dr. Bastian had taken his stand, and, I believe, refuted many of the errors by which the public had been misled.

“The change which has taken place since then in the tone of the English medical journals is quite remarkable, and I am inclined to think that the general confidence of the public in the exactness of Dr. Bastian’s experiments has been considerably shaken.

“In taking up these researches again, I have had occasion to refresh my memory by another perusal of your works; they have revived in me all the admiration which I experienced when I first read them. It is my intention now to pursue these researches until I have dissipated any doubts that may be entertained in respect to the unassailable exactness of your conclusions.

“For the first time in the history of science, we are justified in cherishing confidently the hope that, as far as epidemic diseases are concerned, medicine will soon be delivered from empiricism, and placed on a real scientific basis; when that great day shall come, humanity will, in my opinion, recognise the fact that the greatest part of its gratitude will be due to you.

“Believe me, ever very faithfully yours,

“JOHN TYNDALL.”

We need scarcely say that we read this letter with the liveliest gratification, and were delighted to learn that our studies had received the support of one renowned in the scientific world alike for the rigorous accuracy of his experiments as for the lucid and picturesque clearness of all his writings. The reward as well as the ambition of the man of science consists in earning the approbation of his fellow-workers, or that of those whom he esteems as masters.

Mr. Tyndall has observed this remarkable fact, that in a box, the sides of which are coated with glycerine, and the dimensions of which may be variable and of considerable size, all the particles of dust floating in the air inside fall and adhere to the glycerine in the course of a few days. The air in the case is then as pure as that in our double-necked flasks. Moreover, a transmitted ray of light will tell us the moment when this purity is obtained. Mr. Tyndall has proved, in fact, that to an eye rendered sensitive by remaining in darkness for a little, the course of the ray is visible as long as there are any floating particles of dust capable of reflecting or diffusing light, and that, on the other hand, it becomes quite obscure and invisible to the same eye as soon as the air has deposited all its solid particles. When it has done this, which it will do very quickly in two or three days, if we employ one of the boxes used by Mr. Tyndall—it has been proved that any organic infusions whatever may be preserved in the case without undergoing the least putrefactive change, and without producing bacteria.

On the other hand, bacteria will swarm in similar infusions, after an interval of from two to four days, if the vessels which contain them are exposed to the air by which the cases are surrounded. Mr. Tyndall can drop into his boxes, at any time he wishes, some blood from a vein or an artery of an animal, and show conclusively that such blood will not, under these circumstances, undergo any putrefactive change.

Mr. Tyndall concludes his work with a consideration of the probable application of the results given in his paper to the etiology of contagious diseases. We share his views on this subject entirely, and we are obliged to him for having recalled to mind the following statement from our Studies on the Silkworm Disease:—“Man has it in his power to cause parasitic diseases to disappear off the surface of the globe, if, as we firmly believe, the doctrine of spontaneous generation is a chimera.”

THE END.