Volume 1

Some enumerative studies on malarial fever / by Ronald Ross and David Thomson.

  • Ronald Ross
Date:
[1910?]
Catalogue details

Licence: Public Domain Mark

Credit: Some enumerative studies on malarial fever / by Ronald Ross and David Thomson. Source: Wellcome Collection.

    4/20 page 160
    51 and 38 successful inoculations of men by means of infected blood and infected Anophelines respectively, in not a single one has any exact estimate been given of the numbers of parasites inoculated, or recovered after the lapse of the incubation period; and, though many researches on quinine have been made, we know of none in which its direct effect upon the numbers of the parasites in the patient has been correctly measured. Moreover, the older methods often failed to reveal the parasites at all, unless they were present in large numbers. Hence our first care was to elaborate more exact methods both for detection and for enumeration. This was done early in the year (by R. R. and D.T.)—though we have by no means reached finality yet. The new methods were next employed for all the cases in the Tropical Ward, daily counts of the parasites and often of the leucocytes, together with other estimations, being made (by D. T.). At the same time parallel chemical studies were carried out (by G. C. E. 8.) and therapeutical ones (by D.T.); and the measurements were carefully charted and compared. Even at this preliminary stage the results (which are given at the end of this paper) include more accurate verifications of some old conjectures, and demonstrations of some new theorems. 2. The Detective Method Used.—In the ordinary methods the blood is spread out in a thin film, liquid or dry—1 cu. mm. covering, say, 4 sq. cm. of area. If the field of the oil-immersion lens has a diameter of 0°165 mm., and can be thoroughly searched by the eye in three seconds, about 12 hours’ work would be required to examine the whole of 1 cu. mm. of blood in this way; and if the specimen contains only one parasite it may not, by bad luck, be found until nearly the whole of the area has been searched. We have, therefore, employed the “thick film process” described by one of us (R. R.) in 1903. In this 1 cu. mm. of blood is spread out over only about one quarter of a square centimetre or less, and dried ; the hemoglobin is then gently washed out with water; and the residue,: consisting of parasites, leucocytes, platelets, and the stromata of the red corpuscles, is carefully stained by any convenient method, with or without fixation. By this simple means the whole of 1 cu. mm. of blood can be searched in less than an hour; but the identification of the Plasmodia requires considerable practice. 3. The Enumerative Method Used—The younger Plasmodia are too small to be counted by an ordinary hemocytometer; hence their number has usually been estimated by comparison with the number of red or white cells, the latter figure being determined by the hwmocytometer. This gives a large compound error ; for if ¢ is the percentage error made in counting the red or white cells in one specimen, and e’ is the percentage error made in
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