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of plague by cockroaches is of the greatest importance and the role played by these animals, flies and other non-suctorial insects in the indirect spread of plague infec- tion is one which, from a prophylactic point of view, must never be forgotten,

It is the indirect spread of plague infection which insects accomplish. From what has already been said, it will be evident that suctorial insects are not of such importance as some observers would argue. The indirect spread of plague by insects is requiring of more investigation. By flies, cockroaches, etc, there is no saying how far and how extensive the infection may have reached. All varieties of food stuffs, fruit. clothing, household articles and general utensils are liable to such contamination. Flies, etc. may obtain the specific agents from a variety of sources, e.g., human secretions excretions, rats, or other infected articles, and subse- quently transport these germs of plague to any object upon which they may chance to alight.

III-Relations between insect species and animal species.-These relations have already been discussed, particularly under the subject of fleas Further investigation is necessary but the evidence already brought forward is mostly in favour of definite insect species feeding upon definite animal species. So far as I know the subject has only been investigated in regard to the genus flea The question as affecting bugs, lice, etc., bas still to be unravelled.

IV.-Relation between infected clothing and insects. This is important if we grant that the wounds made in the skin of man by suctorial insects are capable of being secondarily infected through scratching and infected clothing Reliable instances of the occurrence of such a mode of infection in plague have so far not been obtained. The scratching of the skin subsequent to an insect bite may produce secondary inflammations. These are caused by the presence of pyogenic cocci lying deeply in the folds and glandular ducts of the skin. In my opinion, however, it is scarcely possible, or or at least it must be extremely rare, to trace the avenue of infection to such a source,

V.-The Infection of food by insects. This appears to me to be the most important role played by insects in the dissemination of plague infection. The method is an indirect one. The question as to its occurrence has already been muted, particularly in regard to flies, cockroaches, etc., and in Hongkong where insects of all kinds become in themselves pestiferous during certain seasons of the year, including the epidemic plague season, it appears to me not improbable in the light of my results and others, that this part played by insects is dangerous to public health to an extreme degree. That infectious diseases may be spread in this way has already been proved. Flies are undoubtedly carriers of infection fron place to place and are known to be excellent distributers of all varieties of micro- organisms. The spread of typhoid fever by flies in the South African Forces, described by zuM BUSCH and others, and the results obtained by the United States Army Medical Commission in the Spanish American War in regard to enteric fever, are excellent examples of such a spread of infection by insects. Again the experimentally proved occurrence of the infection of food by flies which had previously been in contact with cholera dejecta is another instance of such a

process.

The infection of food by insects would appear to be a cominouer mode of spread of the disease than is generally believed. As has already been men- tioned Pouso's observation of the transmission of plague infection to food by the cockroach is a noteworthy point in this connection. My own experiments showed the presence of plague bacilli in cockroaches, and, as will be seen, plague bacilli have been found in food, namely, rice. It is not improbable that some connection exists between these. At the same time food may become infected through other agencies, namely, contact with plague infected material of varied nature and the secretions and excretions of plague infected man and animals.

My own observations convince me that such a method of transmission of the disease is extremely common. The infection of food and household utensils would appear to be the most important role played by insects in the spread of plague. The experiments made by Professor SIMPSON and myself in this Colony during 1902, point to the importance which must be attached to food as a factor to be reckoned with by those actively engaged in prosecuting the methods for the suppression and prevention of the disease.

WILLIAM HUNTER.