170 Major R. Ross and Dr. D. Thomson. [Oct. 12, 
Other observations are as follows:—(1) By no means every asexual rise is 
followed by a sexual one. In seven cases (13, 19, 25, 26, 28, 31, 33), no 
crescents at all were seen. In Case 13,a negro, 173,400 asexual forms per cubic 
millimetre failed to produce any; and no crescents were observed in another 
negro (Case 28). (2) The number of crescents never exceeded 5 per cent. of 
asexual forms found in the generation which (hypothetically) produced them, 
and were generally in a much smaller proportion. (3) We could find no 
relation to youth, vigour, amount of hemoglobin, duration of infection (from 
3 to 30 weeks), or season of first infection. (4) The daily counts of crescents 
generally show marked daily variations, but we think that after considerable 
doses of quinine have been given for some days these daily variations tend to 
be smoothed out (Cases 16, 18, 22, 24). (5) In Cases 15, 14 and 16 
particularly, a distinct tertian tendency was observed in the daily variations 
of crescents. This appears not to have been previously noticed, but is just 
what would be expected in the case of a tertian parasite; though, of 
course, the curve would be confused in a double tertian. (6) Sometimes 
the crescent curve suddenly rises with great rapidity, reaches its maximum, 
and then begins to fall on the next day with equal rapidity ; though, later, 
the fall often tends to be much more slow (Cases 14, 15, 22, 23), 
especially when the numbers are very small. Apparently, the greater the 
maximum the quicker the fall (Cases 14, 15); and the fall is sometimes 
jagged, with a tertian tendency (zd.). (7) Sometimes the maximum is 
irregularly maintained for a number of days (Cases 16, 18, 24), especially 
when quinine has not been previously given. (8) The crescents remained 
detectable for as many as 31, 32, 32, 35 and 44 days in Cases 20, 22, 23, 24 
and 18 respectively; and finally disappeared (in 1 cu. mm. of blood) in 
Casessle lie 1206. 2Iand 23: 
From these data we think (1) that a varying percentage of asexual 
forms are constantly generating crescents, which, after about 8 to 10 days, 
appear in the peripheral blood. Hence, when the asexual forms remain 
sufficiently numerous for a period, as when no quinine is given, the stock 
of crescents is being constantly replenished. Thus the mortality among 
the older crescents is constantly being compensated for by new arrivals, 
and the total numbers appear to remain constant; an appearance which 
has given rise to the generally accepted hypothesis (perhaps erroneous) that 
the crescents survive for weeks. On the other hand, the sudden rise and fall 
of their numbers seen in Cases 14, 15, 22 and 23 suggest that they really 
survive only for a short time after their appearance in the peripheral blood. 
In Cases 16 and 24, however, a few crescents were still found after quinine 
had been given continuously for 16 to 18 days, suggesting that some of them 
