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.* 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• Nature vol. xv. p. 302, and Appendix II.

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 Bastian; there they continued for three days; they were then withdrawn and placed.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.* " 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. 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 • Nature vol. xvi. p. 24.

Six

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.

In June 1877,—a month later,-Professor Tyndall gave the record of further researches.* These presented additional results as to degrees of temperature requisite for destroying microscopic organisms. It had been already shown that alkaline liquids are more difficult to sterilize, than acid liquids; it was further * Nature vol. xvi. p. 127.

shown that the death point was higher in air, than in water; for Professor Tyndall extended his researches to air, as well as liquid. First dealing with the fluid form, he found germs possessed of vitality so singular that five or six hours of boiling did not destroy them, and in one case eight hours was insufficient for the purpose. In this connection, he came to the conclusion that some germinal orders were more easily destroyed than others.

When dealing with bacteria, he found that they differed from other forms in this, that they rose to the air as if it were a requisite, whereas other germs, such as those belonging to the process of fermentation, could exist without oxygen. This led to an additional form of experiment, with the view of deciding whether bacteria could be destroyed by withdrawal of air; and if so, whether the bacteria would reappear after the existing microscopic life had been stifled. Tyndall began by applying the air-pump. Under this process the bacteria were enfeebled greatly, but not destroyed. Thereafter Sprengel pumps were used, by means of which the air dissolved in the infusions was withdrawn, as well as that diffused in the spaces above. In