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Transactions Texas Academy of Science. 
building, and while some odor can be detected in the immediate vicinity 
of the plant it is not discernible at a little distance therefrom. The filter 
beds are screened gravel and sand and vary in depth from 3^ to 4J feet 
and are two in number, each having an area of two-tenths of an acre. 
It required some time for the beds to attain their full purifying capacity, 
but after the bacterial life had had time to grow within them the work 
has been very effective. Valuable chemical and bacteriological analyses 
have been made by Professors Weems and Pammell, and show con- 
clusively how effective the plant has been. To illustrate, I quote some of 
the figures for its bacterial efficiency, as given in the Engineering Record 
for February 24, 1900. Professor Pammell found that on January 
11, 1899, the manhole above the settling tank had 345,864, the tank 
31,200, and the effluent 8600 bacteria per cubic centimeter. On May 3rd 
the number of bacteria were 194,956 in manhole, 168,600 in tank, and 
11,520 per cubic centimeter in the effluent. On June 28th the tank con- 
tained 1,108,000 bacteria, and the effluent only 2640 per cubic centi- 
meter. On July 5th the manhole had 708,000, the tank 814,000, and the 
effluent 1280 per cubic centimeter. The highest number of bacteria 
occurred on September 27th, the manhole having 9,600,000 and the efflu- 
ent 8160. On September 5th the manhole had 9,000,000 and the west 
filter bed only 600 per cubic centimeter. The average number of bacte- 
ria in the effluent for eleven months was 5127, while the sewage before 
flowing into the tank had an average running away up into the hundreds 
of thousands. Fine millions per cubic centimeter means something like 
144,000,000 per cubic inch — a number that the human mind fails to 
grasp the meaning of. It w r as noticeable that when the temperatures in 
the manhole were highest the number of bacteria were greatest, thus 
showing that temperature has a marked effect upon the growth of this 
low form of vegetable life. Indeed, investigations seem to show that in 
the arctic regions bacteria are nearly or wholly wanting, which would 
indicate that they were not essential to the life of higher organisms, as 
has been repeatedly stated. 
Of course in any method of sewage purification a separate system of 
sewers is required, because it is manifestly impossible to provide, at a 
reasonable cost, facilities for treating, the great amount of rain water 
that occurs at times in connection with the ordinary sewage. 
Now, it has been customary to say all manner of hard things about 
sewer air, or sewer gas, as it is frequently, though incorrectly, called, and 
certainly such odors as a badly ventilated system sometimes exhales are 
neither agreeable nor good for the general tone of the system. However, 
neither chemical nor bacteriological examinations show any evidence of 
disease-producing matter in sewer air, and, indeed, it is often purer than 
outside air in the number of bacteria carried, and those that are usually 
