184 APPENDIX. 



Examination of Water. The bacteriological examination of 

 water is to-day of as much importance as the chemical analy- 

 sis, and must go hand in hand with it. 



At the start we must say that a water containing thousands 

 of germs to the cubic centimeter is far less dangerous than one 

 containing but two germs, if one of these two be a typhoid ba- 

 cillus. It is not the number that proves dangerous, it is the 

 kind. 



If a natural water contains more than 500 germs to the cubic 

 centimeter, it were well to examine its source. 



Bacteriology performs the greatest service in testing the devices 

 which are intended to render water fit for drinking. 



As a diagnostic aid the examination is of but little use. An 

 epidemic of typhoid fever occurs, the water is suspected, an ex- 

 amination is undertaken ; but the days of incubation and the 

 days passed before the water is analyzed have given the typhoid 

 germs, if any had been present, ample time to disappear, since 

 in water that contains other bacteria they live a very short time 

 only. Again, the water tested one day may be entirely free and 

 the next day contain a great number, and before the typhoid 

 germ can be proven to be present in that particular water, the 

 epidemic may be past. 



Purity of Waters, The purest water we have is the natural 

 spring water water that has slowly filtered its way through 

 various layers of gravel and sand and comes finally clear and 

 sparkling from the ground. It is without germs ; but let such 

 a water stand walled up in cisterns or wells, it becomes as 

 surface water, open to all sorts of impurities, and the bacterial 

 nature of it changes every moment. 



Artesian or Driven Well. The driven well will secure to a cer- 

 tain extent a pure water. It is the only form of well or cistern 

 that will insure this, since the water does not become stagnant 

 in it ; but it may connect with an outhouse, the soil being very 

 loose, allowing the products of germs of refuse water to find their 

 way into the well. If a chemical examination shows increased 

 amounts of chloride of sodium, a contamination can be mooted. 



Filtered Water. Dangerous as surface water is, the greater 

 quantity used, is such : the inhabitants of larger towns and cities 



