Observations on the mechanism of the transmission of plague by fleas / by A.W. Bacot and C.J. Martin.

  • Bacot, Ada W. (Ada White)
Date:
[date of publication not identified]
Catalogue details

Licence: Public Domain Mark

Credit: Observations on the mechanism of the transmission of plague by fleas / by A.W. Bacot and C.J. Martin. Source: Wellcome Collection.

    9/42 page 426
    emulsion was dabbed over it with a pledget of cotton-wool. The rats were immediately returned to separate cages. A third control series, Series C, contained 13 rats, which were treated in the same manner as those of A, with the omission of the flea-punctures. Most of the rats promptly eked off the spleen-pulp or emulsion which had been applied. Series A consisted of ten rats, of which nine died of plague it in under 3 days. Series B consisted of 23 rats, of which five died of plague. Series C consisted of 13 rats, none of these contracted the disease. Four out of the nine rats of Series A which contracted the disease displayed phlectenules—in two cases arranged in a ring corresponding to the situation of the punctures. All showed buboes either in the axillae or groin. The experiments show a striking difference in the incidence of infection. This might be accounted for either by variation in the number of bacilli deposited or in their virulence. We incline to the latter interpretation, as we endeavoured to arrange that the amount of bacilli applied should be of the same order. We have not actually determined the relative virulence of the two kinds of organisms, as this could only be done by experiments on a long series of animals. One significant difference in the properties of the two strains of organisms was, however, observed. When mixed with a drop of our own blood, and incubated for 15 minutes between a slide and cover glass, as in the original method devised by Leishman for the quantitative estimation of phagocytosis, the bacilli direct from the spleen were not taken up by the phagocytes, whereas those from tte flea’s stomach were freely ingested. The experiments were performed as follows: to obtain bacilli from the spleen a piece of the organ was minced up with 85 °/, NaCl solution and centrifuged at a low speed until the tissue cells and blood corpuscles were deposited. After centrifugation the plague bacilli were partly in suspension and partly in a loose deposit on the surface of the cells. This loose deposit was dispersed into the medium by gently shaking, without disturbing the cells, etc., and pipetted off. The emulsion was centrifuged at a high speed, the supernatant fluid, which now consisted of bacilli with an occasional cell, removed, and the deposit emulsified in fresh saline. The emulsion consisted only of single bacilli, The number of bacilli per c.c. were determined by counting in a Thoma Zeiss cell,
    digitised image 1
    digitised image 2
    digitised image 3