SWIMMING-POOI. SANITATION 
263 
of the water. It would seem that 500 bacteria at 37° C. is a more 
reasonable requirement for pool water and that the colon bacilli 
should be absent in one cubic centemeter. 
The environmental conditions in the pool are such that the 
growth of the ordinary water bacteria is much stimulated. Tem- 
perature and food conditions enable the few organisms remaining 
after disinfections to multiply rapidly and give aftergrowth rep- 
resented by large numbers. There is no special reason to regard 
these bacteria as pathogenic, and unless the bacterial count at 
37° C. is high and colon type organisms are present, there is 
probably no reason to think that a high 20° C. count has any par- 
ticular significance. Some workers have entirely omitted the 
enumeration at 20° and neglected the information which the 
20° C. count may give at times. 
We have found the 20° count subject to sharp fluctuations, 
although likely to show up in the worst manner within the first 
few days after the pool is filled. PVom the operation standpoint 
we have not paid great attention to this first aftergrowth. When 
the pool shows a high 20° C. count after having been in use 
some time and we find it difficult to reduce it promptly we take 
it as evidence that the food conditions are too advantageous. 
We may then advise that the pool be emptied. 
We watch the 37° C. count more zealously than we do the 
20° C. ones. While about 20 per cent of the latter have passed 
the limits which we have arbitrarily set as desirable, only about 
5 per cent of the former have passed the limits. 
The presence of gas-formers and acid colonies is regarded as 
most significant of all. If these are persistent, even in 10 c.c. 
quantities of water, the advice is given to empty the pool. The 
gas-forming organisms have not all received the confirmatory 
test for B. coli. Of those that have been specially tested about 
one-fourth have proven to be 5. coli. It should always be kept in 
mind that these figures give the results on samples taken after 
use, not on the pool as it is after having received purified water 
all night. Fresh contaminations are considered to be more dan- 
gerous than older ones. 
In the table given the figures for purification by filters alone 
may be misleading. They appear' to show superior results. As a 
matter of fact only the instructors were using the pools at that 
time and the bathing load was only about 1 per cent of the normal 
load. Attention is called to the high percentage of positive tests 
for gas- and acid-forming bacteria found. Our experience has 
