510 REPORT OF THE HARVARD AFRICAN EXPEDITION 
examined. The solid tablets contained one per cent of available chlorine and the 
disintegrated tablets slightly more than this.” Inasmuch as the tablet originally 
contained four per cent of the acid which is the active chlorinating substance, and, 
inasmuch as this acid should contain about twenty-five per cent of available 
chlorine, there seems to have been no appreciable deterioration of the halazone. 
Mr. Clark’s report upon the Army ampoules of calcium hypochlorite is in 
contrast to these findings. Of the two samples tested, he said: ‘‘The first con- 
tained 13.7 per cent, and the second 14.4 per cent of available chlorine,’ whereas 
“chloride of lime contains practically 34 per cent available chlorine; hence this 
material had decomposed and, in fact, when the ampoules were opened they ex- 
ploded with loss of chlorine.” 
Mr. Clark reported on the ampoules of sodium thiosulphate as follows: 
“Two samples analysed. The material had lost some water of crystallization 
but was of full strength.” 
Regarding the orthotolidine, he said: ‘‘Two ampoules were broken open and 
poured into 50 ¢.c. of distilled water each. Chlorine water added to faint yellow 
colour required 0.03 ¢.c., which is equivalent to 0.008 part chlorine in 100,000 in 
both cases. Good quality.” 
Of Burroughs Wellcome & Co.’s tabloids of potassium iodide and starch, after 
describing his tests, he remarked: ‘It is evident there has been some decompo- 
sition of this mixture, as would be expected.” 
SCHISTOSOMIASIS 
It is well known that the cercariae of Schistosoma which fail to find a host do 
not long survive, and that water containing them, if free from infected snails, 
becomes safe within less than 48 hours. Similarly, it is known that the cercariae 
are killed in a short time when the water has been heated to 50° C. (122° F.). 
To be quite safe, it is well to have the bath water heated to 60° C. (140° F.). 
I have no information about the effect of chlorination upon cercariae, and do 
not know whether water treated as above described with chlorinating substances 
is safe for drinking in a district where schistosomiasis is found. When in doubt 
we boil the drinking water (see also page 229 of this Report). 
TURBID AND Muppy WATER 
Since returning from Africa I have discussed the problem of clarifying drink- 
ing water in the field with Dr. Milton J. Rosenau, Professor of Preventive Medi- 
cine and Hygiene, of the Harvard School of Public Health. He proposed the 
following procedures : — 
A. (1) Let the water stand for an hour or more. Then pour it off, leaving 
behind the mud which has settled to the bottom. 
(2) Strain through several layers of cloth, e.g., Canton flannel. 
(3) Filter through Berkefeld candle by means of a pressure pump. 
When this process has been carefully performed in a cleanly manner, neither 
boiling nor chlorination would be necessary. 
The Berkefeld candle is cleaned by scrubbing or scraping the inner or outer 
