238 ESSENTIALS OF BACTERIOLOGY 



of an aspirator or air-pump is used to accelerate the pas- 

 sage. 



These porcelain cylinders can easily be sterilized ancl the 

 pores washed out. 



All the cylinders or bougies are not germ proof, so that they 

 must be tested, and most of them must be cleaned every 

 fourth day. In recent years a number of organisms have 

 been suspected of being so minute as to pass through a 

 Berkefeld or Pasteur filter. At least the poison or virus is 

 filterable, and, therefore, we cannot regard these as abso- 

 lutely safe. 



Boiling as a Means of Purifying. The only safe measure 

 in times of epidemics and with waters of unknown composi- 

 tion is boiling, not only of the drinking water, but all water 

 used for domestic purposes; and this should especially be 

 done in times of typhoid and cholera epidemics. 



Varieties Found in Water. The usual kinds found are 

 non-pathogenic, but, as is well known, typhoid, cholera, and 

 dysentery are principally spread through drinking-water, 

 and many other germs may find their way into the water. 

 Some of the common varieties give rise to fluorescence or 

 produce pigment. 



Eisenberg gives 100 different varieties as ordinarily found. 

 Other intestinal diseases besides those mentioned above are 

 supposed to be water borne. Diarrheas in epidemic form 

 may come from suddenly changing a public supply, and 

 the presence of the Bacillus coli communis means sewage 

 contamination or fecal contamination; such contamination 

 may come from the droppings of birds or other animals and 

 need not necessarily imply human sewage, but 10 colon 

 bacilli in i c.c. water is a serious pollution. Ice supplies 

 require the same supervision as water supplies, for many 

 bacteria, like the typhoid bacillus, retain their vitality for 

 weeks after freezing. 



Method of Examination. (After that suggested by the 

 American Public Health Association, 1912 report.) Since 

 the germs rapidly multiply in stagnant water, an examina- 



