The prevention of malaria.

  • Ronald Ross
Date:
1910
Catalogue details

Licence: In copyright

Credit: The prevention of malaria. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

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    the time, or less, required for an ordinary preparation — but the parasites, especially P. vivax, are apt to be overlooked unless the observer trains himself in the work. Originally I washed out the haemoglobin with water and then fixed and stained the residue as usual; but later I obtained better results by washing out with eosin solution, washing this off, and then passing over a weak solution of methylene blue. R. Ruge, however, advocates the former procedure [1903], and L. Rogers [1908, p. 17] prefers first to fix and stain, and then to wash out the haemoglobin with a very dilute solution of acetic acid—which leaves the outline of the haematids without obscuring the view. All these methods are useful. Sediment and overstaining of the stromata are to be avoided, and the film should not be too thick. (2). Enumerative methods.—Very rough ones are now in use. We count the number of parasites in a given number of fields of an ordinary preparation—giving an enormous possible error, because we do not know the amount of blood in each field. Or we count the number of parasites found near a given number of leukids, the latter being counted by a haemocytometer. Here the total estimate is the product of the two partial counts; and if the errors contained in the latter are both positive or both negative (which should occur in half the estimations), the total error may again be enormous. Direct counting by the haemacytometer is far from easy in the case of small parasites, owing to the depth of the fluid examined. Since the beginning of this year (1910), the Advisory Committee of the Tropical Diseases' Research Fund (Colonial Office) have granted considerable funds for the accurate study of cases of malaria in Liverpool, and Dr David Thomson and myself have commenced this study by elaborating improved enumerative methods based on my thick-film process. A measured quantity of undiluted blood is made into a thick-film preparation, and the total number of parasites con- tained in the whole of it is carefully counted. The quantity of blood used is measured by means of a graduated pipette or capillary tube. It is necessary that this tube should have a very fine calibre to allow a small quantity of blood, such as 1 c.mm., to occupy a sufficient length of the tube to permit of accurate measurements being made. Thus a tube of 180/i in diameter, ind of 4 cm. in length, will contain roi8 c.mm. (say 1 c.mm.) of blood. Dr Wakelin Barratt points out that any one can make a suitable pipette by drawing out a fine capillary glass tube, measuring its calibre by the microscope, and calculating the length required to contain the given volume (area of