160 Major R. Ross and Dr. D. Thomson. [ Oct. 12, 
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 hemocytometer. This gives 
a large compound error; for if e is the percentage error made in counting 
the red or white cells in one specimen, and e’ is the percentage error made in. 
