that malaria might be transmitted by a biting insect. He was, indeed, engaged upon experiments with mosquitoes, and had nearly satisfied himself that malaria was thus transmitted, when Ross published his results. Koch was, however, largely instrumental in showing that the three types of malaria were associated with three distinct parasites, and that none of these were infective for the lower animals, a result of great importance, from the point of view of malaria prophylaxis. He also cleared up the difficulty as to the reservoir of the disease in a population the adults of which could not be found to harbor the parasite by showing that the young children, even to the extent of 90 to 100 per cent, were infected.

In 1901 Koch reported to the British Congress on Tuberculosis the results of experiments which he had carried on during the preceding two tears in conjunction with Schutz upon the pathogenicity of the human tubercle bacillus for domestic animals. Briefly stated, Koch's main conclusion from their experiments was that human tuberculosis differs from bovine and can not be transmitted to cattle. The far more important question: "Is man susceptible to bovine tuberculosis?" was then considered. No direct experimental proof of this converse proposition is possible, but from the fact that men-and particularly children-consume large quantities of bovine tubercle bacilli in milk, and yet tuberculosis of the intestine is rare, Koch concluded that man is little if at all susceptible to the bovine variety of the bacillus. He pointed out that the question whether man is susceptible to bovine tuberculosis at all was not decided, but expressed the belief that infection of human beings is of so rare occurrence that it is not necessary to take any measures against it. It was the last conclusion that caused so much consternation, as most countries were embarked in considerable expenditure with a view to minimizing the chances of infection by milk and meat. Koch may have been unwise in stating his views, but he did so with the conviction that bovine tubercle is not an important source of infection, and with the earnest desire that we should not squander our energies in subordinate directions, but should concentrate them in efforts to diminish man-to-man infection through the respiratory tract.

The importance attached to a considered opinion of so distinguished an authority led to the appointment of numerous commissions of inquiry in Europe and America. Of these the work of the English Royal Commission has been the most extensive. These investigations have shown that the sharp distinction between the two varieties though usually manifest, is not so absolute as Koch supposed, and that bacilli of the bovine type are not so uncommonly found in human infections as he was led to believe. The frank expression of opinion by Koch on this subject has been the stimulus for an enormous.

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amount of valuable work in connection with tuberculosis throughout the civilized world, but the relative importance of infection from one another through sputum and from bovines through dairy produce is still an open question, and will not be settled for many years to

come.

Before closing this sketch of his life work, it remains to add a few words upon Koch as a teacher. In 1885 he removed from the health department and became a professor in the faculty of medicine and director of the new hygiene institute, attached to the University of Berlin. Here, with the help of his assistants, numbers of those who later became leading bacteriologists in all countries were trained in his methods and endowed with some portion of his enthusiasm and earnestness. The admiration with which he was regarded by his pupils, and the absolute faith which he inspired, amounted in many cases to actual worship, and afford further evidence of the essential greatness of the man.

Amongst the numerous honors conferred upon him by scientific and academic bodies throughout the civilized world was the foreign membership of the Royal Society, to which he was elected in 1897.

There have no doubt been many discoverers as great as Koch, but it must be seldom that one has been so individually associated with the development of a science. Bacteriology has to so great an extent grown up around Koch that the title "Father of Bacteriology" has been conferred upon him by his admiring compatriots.

SIR JOSEPH DALTON HOOKER, O. M., G. C. S. I., F. R. S.,

1817-1911.1

[With 1 plate.]

By Lieut. Col. D. PRAIN, C. M. G., F. R. S.,
Director of the Royal Botanic Gardens, Kew.

The most distinguished son of a very distinguished father, Joseph Dalton Hooker, was born at Halesworth, in Suffolk, on June 30, 1817. Early in 1820 his father was appointed by the Crown to fill the chair of botany in the University of Glasgow, a post which he held until, in 1841, he became director of the Royal Gardens at Kew. As a consequence Hooker was educated in Glasgow, passing through the high school to the universiy, from which he obtained the degree of M. D. in 1839. Devoted as a lad to the reading of works of travel, we learn from Hooker himself that he was especially impressed by Turner's description of the Himalayan Peak of Chumlari, and by the account of the Antarctic island of Kerguelen contained in Cook's voyages. An opportunity of investigating the latter came to him very early in his career. When he completed his medical studies, Hooker entered the Royal Navy as an assistant surgeon, and was gazetted to the Erebus, then about to start, along with the Terror, on the famous Antarctic expedition led by the eminent navigator Sir James Clark Ross. Throughout this expedition the young assistant surgeon held the post of botanist, and during its three years' cruise in the southern seas he was able to visit New Zealand, Australia, Tasmania, Kerguelen, Tierra del Fuego, and the Falkland Islands, amassing large collections and acquiring a vast amount of botanical information.

Shortly after the close of this expedition, Hooker, in 1843, became assistant to Graham, then professor of botany in the University of Edinburgh, and in 1845, when Graham was succeeded by the elder Balfour, Hooker was appointed botanist to the geological survey of Great Britain. Much of his time during this period was devoted to the preparation for publication of the results obtained during the course of his Antarctic voyages. But in 1847 this work was temporarily suspended, and his appointment on the geological survey was

1 Reprinted by permission from Nature, London, Dec. 21, 1911, No. 2199.