Report, Medical Officer of Health, on rat repression in the City 1920.

  • City of London (London, England). Corporation of London.
Date:
[1920]
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Report, Medical Officer of Health, on rat repression in the City 1920. Source: Wellcome Collection.

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    12 At present I know of no infection which would answer these requirements. As already stated, the various viruses which have been used are known to introduce more or less fatal epidemics among rats, but the disease is not fatal to all, and some even acquire immunity and act as carriers with possible danger to public health, since the organisms used are certainly not harmless to human beings. Plague is notoriously fatal to rats, so much so that in plague-infested areas rats desert the district and so introduce the disease to a previously non-infected area. Plague is, of course, a fatal disease to which human beings are liable, and therefore cannot be used. I do not consider that possibilities in the above direction have been exhausted. (30) (ii.) An attempt has been made to reduce the number of rats by the introduction into a district of antagonistic species not normally indigenous to that area. The introduction to new areas of animals which have successfully acclimatised themselves to their new surroundings has not invariably been devoid of objection, e.g., rabbits in Australia, in which instance the introduced animal has constituted itself practically a plague. The mongoose was also introduced into certain parts of the West Indies to diminish the rat. It certainly effected its purpose, but I understand that this animal is now almost as objectionable as the rat, for the rat has acquired arboreal habits, and by limiting the supply available for the mongoose, the latter has turned to the chicken runs. 1 have also been informed that the mongoose causes considerable damage to the sugar canes. In this country the weasel, stoat and owl, and perhaps the hawk, are the known enemies of rats, but none of these animals or birds could be used in buildings. Some use might be made in City warehouses of the mongoose, and I attach a description by Mr. Jennison on how the mogoose should be tended. (31) (iii.) The introduction of some factor which will interfere materially with rat propagation, as, for example, that which would result from a disturbance of the numerical sex relationship has been advocated; this latter under the designation of the Rodier System. This method is advocated by Rodier for use against rabbits, and he claims with success. As regards the application in the case of rats, the only experience in this country I am acquainted with is that gained by Mr. Jennison at the Zoological Gardens, Manchester. I believe that it is possible for animals in the wild state to change from the monogamous to polygamous state, but not the reverse. Take for instance the bird of paradise, which was formerly monogamous, but to-day, owing to the slaughter of the male birds, a polygamous state has developed. I believe also that limited polygamy in nature can develop into increased polygamy under certain forms of selection, as for example in the case of sheep. The herds of wild sheep in the Rockies are constituted in the proportion of one male to eight females, but in the sheep flocks in this country the average is about one male to 30 females. The introduction of an additional ram to flocks of sheep results in interference with the number of lambs produced, and similarly one finds that in a pigeon loft, free cock birds will materially affect the breeding in that loft—three odd cocks will ruin the breeding of three nests. In a poultry yard excess of cock birds will materially interfere with, if not entirely stop, the laying of eggs by the hens of that community. (In this connection 1 am informed that the male bird of the Jungle Fowl controls four or five hens, whilst in the ordinary domestic variety the hens may number up to 20.) For somewhat similar reasons cock pheasants must not be in excess in the nesting season, so they are shot off whilst the hen birds are spared at the end of the ^shooting season. Also a comparatively small proportion of males among guinea pigs kept in confinement together results in a reduction in numbers bred and the final extinction of the females. These facts tend to show that sexual relationship can b.e extended from the limited range to the wider range, but when once the wider range has become established, reduction of females and proportionate increase of males results in conditions which are unfavourable to the procreation of the species.
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