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.* 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." 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 potasse was kept enclosed in another part of the tube, ready to be added

* Contribution to Royal Society of London. Nature xv. p. 302, Feb. 1, 1877.

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. 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 • Nature vol. xvi. p. 24.

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.