The controversy on this subject was at its height in the years 1876, and 1877, having a large amount of most careful and difficult experiment devoted to it. The result has been a valuable addition to scientific knowledge as to the vitality of germinal forms, and a quietus to theories as to "spontaneous generation."
The direct object placed before the scientific mind when the discussion arose was this,—to ascertain whether an origin of vital activity could be observed in the midst of materials from which all germinal forms of life were certainly excluded.
The selection of materials to experiment upon was for a time according to the fancy of the experimenter. It was not proposed that a vacuum should be made by withdrawal of all air from a glass vessel, thereafter watching for the appearance of some organic form. Nor was it suggested that pure water might be taken from a spring, and boiled, and left standing under daily observation. A great variety of materials was selected to provide an infusion which might afford the conditions for application of scientific tests. In this way the following materials were used and tested, infusion of turnip, of pounded cheese, hay, meat, fish, besides egg-albumen, blood, and urine. Vegetable productions, animal tissue, and secretions of the human body closely connected with vital processes, were thus subjected to test. In the history of investigation, attention ultimately concentrated on the infusion of hay and on urine. Observations were conducted in Paris and London; results were published from time to time; singular divergence became apparent in these recorded results; this led to controversy, which became so keen, that the Academy of Sciences in Paris appointed a commission of three to adjudicate upon a challenge given by M. Pasteur of Paris to Dr. Bastian of London; which Commission met in Paris on 15th July, 1877, but never adjudicated in the matter.[G]
The perplexities encountered in conducting observations arose chiefly from two causes: the difficulty of ascertaining the temperature at which living organisms were certainly destroyed, and the materials sterilized; and that of guarding against interference with this state when established, by contact with the atmosphere. The latter perplexity, involving much care, skilful manipulation, and mechanical contrivance, was at last overcome by the construction of glass tubes, separating for a time the distinct materials, with facility for their mixture at the proper moment without contact with the air.
The true scientific difficulty, however, was determination of a reliable test for destruction of germinal forms, either adhering to the materials, embedded in them, or floating in the atmosphere. The history of observations bearing on this question is deeply interesting. In the earlier tentative experiments, the material placed under observation was boiled; it was concluded that no vital organism could endure this process; and the material was kept for a time in a temperature of from seventy to eighty degrees Fahr., which was regarded as favorable to the development of life. In process of time, a deposit appeared in the tube, and this when examined under the microscope was found to contain bacteria,[H] living, moving germinal forms so minute as to require high magnifying power for their discovery. Here then was "spontaneous generation." Who could be so credulous as to believe that minute organic forms could live through the boiling process? If this appeared too absurd to fancy, then spontaneous generation, or actual origin of life out of non-organized matter, must be held to be established. It was only the audacity of prejudice, and hopeless alienation from the "advanced thought" of the time, which could induce any one to doubt, in face of these experiments, carefully recorded and published.[I] Scientific observers of great experience and reputation felt it needful to express themselves with caution, leaving results to be tested.
A considerable number of investigators began to turn their attention to the subject, and a period of seven years was occupied before the results became so certain as to be practically final. Pasteur, Pouchet, and Joubert were at work in France, Crookes, Child, Beale, Roberts, Bastian, Tyndall and others in England.
All experiments concentrated upon certainty in sterilizing the substance operated upon. Pasteur pointed out that the chemical properties of the infusion affected the vitality of the microscopic germs inclosed in it; and Roberts at a later stage confirmed this by independent investigation, proving "that slightly alkaline liquids are more difficult to sterilize by heat than slightly acid liquids."[J] In this way, it was shown that distinct records of temperature were needful, greater intensity of heat being required in some cases than in others, in order to secure destruction of germs. The facts were illustrated by hay infusion, "the acid infusion invariably remaining barren after a few minutes' boiling, and the neutralized infusion invariably becoming fertile after a similar boiling."[K] The neutralizing element was liquor potassæ, and the next question started was this, Did the liquor potassæ enable the germs to live longer under the boiling process, or did its infusion operate so as to originate life where germs no longer had any existence? A contrivance was adopted by which the boiling could be applied to the hay infusion, while the liquor potassæ was kept enclosed in another part of the tube, ready to be added without exposure to the air, after the boiling process was over. When added in this way, "the liquor potassæ had not any power to excite germination:" the expectation that a certain mixture of acid and alkali would originate life was disappointed; all the earlier experiments were discredited. Still, some clung to their expressed belief, for there is a prejudice of advanced thought, as there is a prejudice of old beliefs. Tenacity of avowed opinion, with strong love of research, prolonged the inquiry, and led to more decided evidence.
The controversy was conducted by Dr. Roberts against Dr. Bastian, while all the experiments of Professor Tyndall were converging upon the same conclusions as those reached by Roberts.[L] That Bastian had obtained bacteria after boiling, admitted of no doubt, and he naturally clung to this fact as encouraging; others regarded it as only misleading. Bastian maintained that the alkali had a positive power of originating life, and stated one hundred and twenty-two degrees Fahr. as favorable to the appearance of life. Roberts took ten examples of sterilized urine, and twenty-nine examples of fermentible liquids which had remained over from the earlier experiments of 1873-74, and these thirty-nine examples were subjected to careful experiment and observation. In the first ten cases, the tube was heated in oil for fifteen minutes up to two hundred and eighty degrees Fahr.; the ten tubes were then set in a warm place (from seventy degrees to eighty degrees Fahr.) for a fortnight; the contents were transparent; the alkali was then allowed to mingle with it, and the tubes were placed in an incubator kept at a temperature of one hundred and fifteen degrees Fahr.; at the end of two days there was a sediment, and the liquor was clear; the tubes were replaced in the incubator, the temperature being raised to one hundred and twenty-two degrees Fahr. as recommended by Dr. Bastian; there they continued for three days; they were then withdrawn and placed under the microscope, but no trace of living organism was found either in the fluid or in the deposit under it. The twenty-nine cases, including a variety of vegetable and animal preparations were next treated in like manner, and with like results. Tyndall's experiments were reported to the Royal Society of London at the same time, with exactly the same result. M. Pasteur had previously reported to the Academy of Sciences in Paris to the same effect. It was thus proved by a mass of evidence that if proper precautions were taken to destroy germinal forms, no mixture of alkali with acid, whatever the variety of materials selected, was adequate to produce life.
A few months later than the communications of Roberts and Tyndall, that is, May, 1877, the results of ten years' experiment, first by Mr. Dallinger himself, and thereafter by Mr. Dallinger and Mr. Drysdale conjointly, were communicated to the Royal Institution, London, on "the origin and development of minute and lowly life forms.[A]" The purpose of these experiments was to watch the growth of the minutest germs, capable of being seen only under a powerful microscope, putting to actual test their tenacity of life. The largest objects were one-thousandth of an inch, the smallest, the four-thousandth of an inch. Six distinct forms were selected for observation, and their history was made out. A magnifying power of five thousand degrees was used. In the glairy fluid a monad larger than usual seized on a smaller; they became fused after swimming about together; the single object then appeared a motionless spec; this proved to be a sac, from which at the close of a period varying from ten to thirty-six hours, it burst, and young spores became visible in the fluid, which were kept under observation till they reached maturity. Special interest was connected with these observations not only as illustrating the growth of spores, or germs; but as allowing application of the test of heat at different stages of growth. When this test was applied, it was found that one hundred and forty degrees Fahr. was sufficient to cause the death of adults, whereas the young spores were able to live notwithstanding the application of three hundred degrees Fahr. for ten minutes. In this direction fresh discovery was to be made.