1887.] MICROSCOPICAL JOURNAL. 129 
Quantitative variations in the germ life of Potomae water during the 
year 1886.* 
By THEOBALD SMITH, M. D., 
OF WASHINGTON, D, C. 
The value of the so-called biological analysis of drinking water—the quan- 
titative and qualitative determination of bacteria present—is still very un- 
settled. Recent investigations certainly have not contributed toward a élearer 
understanding of the problem, but have made it more complex. | Meanwhile 
statistical determinations cannot be amiss in aiding investigators in inter- 
preting their own results. It is from this point of view that the following 
statistics are published, without any attempt at estimating the quality of the 
water therefrom. 
The water was drawn from a faucet in the basement of the Agricultural 
Department building, which was constantly in use, so that there could have 
been no stagnation of water in the smaller pipes. It was immediately exam- 
ined according to the method of Koch—two gelatin plates being always made 
from the same sample of water. This was measured with flamed glass pipettes 
without being diluted. The pipettes} were graduated by determining accu- 
rately how many drops of distilled water were 1equired to make 1 cc. If 51 
drops were necessary, and only 8 added to the gelatin, .8- cc. was considered 
taken. This method is far simpler than the one which insists upon dilution, 
unless the number of bacteria be very large. 
From o.1 to 0.5 cc. of water was added, according to the probable number 
of bacteria present. The culture medium was the well-known beef infusion 
peptone gelatin, containing ro per cent. gelatin. There was always a close 
agreement between the two parallel plate cultures made from the same sample. 
As to the results of the year’s observation, we first observe from a glance 
at the table that the number is highest in winter, in spite of the fact that heat 
greatly favors, and cold checks, multiplication. 
Table giging the Monthly Average Number of Bacteria found in one Cubic Centi- 
meter of Potomac Drinking Water during 1886. . 
Number of Rainfall Number of Rainfall 
1886. observations. AVETAzE: (inches). 1886. observations. AVETAEE: (inches). 
A EPNIAIY ealeony ee iennsanaesecse 2 3774 3.46 AU BUS tic doce ices sob avcsetas I 254 1.03 
[Dte|syeteinny corcooniscencel eres ne 2530 2.79 DSeptemabernssecscen cocescesty 2 178 1.04 
VEATCH aecncssscesctevorsssscs? 5 1210 4.16 October... 5 75 2.31 
April.. Le a 1521 4.21 November.. bie: 116 3.69 
May .. rep 8} 1069 7.77 WEGeMDereeecsrcrseecccrte 2 967 3-07 
WW ie Sor Per lice eo deceeeriaeoneS 2 348 4.98 1887. 
TI EV eciocrigncteet aececeporeeceene 2 255 8.42 January id-pcscsecesccsseee 2 882 2.19 
This anomalous condition is not so difficult of explanation. In the winter 
the water as it reaches the city is more or less turbid, and, when shaken, 
clouds, composed of very minute particles, are seen. These will pass through 
ordinary filter paper, and when gathered together, as in distilling water, the 
residue is made up of reddish earth. This turbidity, most pronounced 
in winter, gradually disappears toward summer, when the water becomes 
very clear and limpid. The number of bacteria varied with the change in 
turbidity, being highest when the suspended matter was most abundant. 
* Reprinted from Medical News, April 9, ’87. 
t The pipettes are easily made by drawing out, in the flame, the middle point of a piece of glass tubing about 
15 cm. long and 6-7 mm. in diameter, until a narrow tube is formed $ to x mm. in diameter and about 30 cm. 
long. This is broken in the middle to make two pipettes. If the capillary tube be drawn out to the above 
size, each drop will equal from ;\5 to gy of a cc., the exact size being determined for each pipette. Into the 
other end a plug, preferably of glass wool, 2 to 3 cm. long, is introduced, and the bulb of a medicine dropper 
drawn over the tube to give the necessary aspirating force. Immediately before use the pipette is thoroughly 
flamed, beginning with the glass-wool plug while it is held with the bulb between the fingers. Care must be 
taken lest the heat be too great, and change the form and size of the orifice, If any doubt exists as to this point, 
it is best to graduate the pipette again 2/fey use, and with the sample of water to be examined if the latter 
should vary much in its specific gravity from distilled water. 
