before the Institution, and he asked the members to read the explanation, given in the clearest possible language, as to why a specimen which was subjected to repeated reversal of stress must, according to the teaching of microphotography, inevitably fail at a lower stress than under the ordinary test. A certain number of crystals always occupied an unfavorable position, and they yielded at a certain stress before the other particles yielded. If they were allowed to remain in that new position they might possibly fix themselves there, but if the stress was reversed the movement found these particles in a weakened state; and if it was again reversed they again gave way, and thus threw a greater stress on the surrounding particles, and at last caused fissures to form and a fracture to take place. This was the ultimate cause of the apparent crystallization of a fractured specimen. Engineers used to be taught, only a little while ago, that a metal crystallized after a certain time when it was subjected to alternating stresses. A direct contradiction of that teaching was contained in Dr. Rosenhain's lectures. As a matter of fact it was not a crystallization. The crystals were there before, and they were there afterwards. The facets which had a crystallized appearance were facets of fracture which were gradually produced by the alternation of stresses, and thereby the breaking down of the specimen was obtained. He thought the members would agree with him that one thing was very apparent from the paper and the discussion, namely, the limited extent of our knowledge of the subject. After listening to the remarks of the authors and of the gentlemen who had taken part in the discussion, the members must feel they had a great way yet to go before the real nature of the many phenomena of the resistance of metals was understood. He trusted that more experiments would be carried out, with the object of teaching the members to realize what was actually going on in the materials they had to use, and at the same time he desired to thank the authors for their extremely valuable experimental work, which was of a character to aid the building up of a sound theory of the subject.

ROBERT KOCH, 1843-1910.1

[With 1 plate.]

By C. J. M.

Prof. Koch was one of the great discoverers of medicine. His researches have exercised a profound influence not only upon the development of medical science, but also upon the welfare of mankind.

Born in 1843 at Klausthal, and educated at the Gymnasium, he studied medicine in Göttingen from 1862 to 1866. After a short period as assistant at the hospital in Hamburg, he commenced practice in Langenhagen, Hanover. In 1867 he removed to Rackwitz, in Posen, where, in addition to carrying on a country practice, he found time to study for and to take a degree in physical science. In 1872 he became district surgeon in Wollstein. It was while at Wollstein that Koch's attention was first seriously turned to the interpretation of infectious diseases. The study of the work of Pasteur and his pupils on fermentation and putrefaction, and of Lister on the antiseptic treatment of wounds, led him to the conclusion that the etiology of infection was not to be found in miasmata from the soil, as commonly entertained at this time, but much more probably, in the entrance into the tissues of microbes, and their multiplication therein.

At the time Koch commenced to investigate infectious diseases, bacteriology had become differentiated as a department of scientific inquiry, but the methods proper to the new science were not developed and, although a number of cardinal facts had been brought to light, knowledge on the subject was chaotic, and advance temporarily checked. Diseases of man and animals presented unlimited problems, but the means to attack them were lacking. The means which led to the next important advances were supplied by Robert Koch, who possessed that rare combination of intellectual qualities which enabled him, not only to see what was the next question to

1 Reprinted by permission from Proceedings of the Royal Society, London, Series B, vol. 83, No. B 567 May 31, 1911, pp. xviii-xxiv.