138 THE AMERICAN MONTHLY [Aug 



that the presence of 0-05 of organic matter per 100,000 

 parts is a negligible quantity. Some time ago a water 

 was described as containing 1 grain (0-0648 gramme) of 

 organic matter in 5000 tumblers,/, e., one 5-OOOthofa 

 grain (-00001296 gramme) per tumbler. Now, granting 

 that this organic matter represented bacteria, and in 

 weight they resembled the Staphylococcus aui'eus, it 

 follows that each tumbler contained the alarming pro- 

 portion of over 518 thousand typhoid bacteria. If we 

 go a step farther and consider the alarming rate at 

 which the cholera bacteria multiply in the blood of a 

 healthy rabbit, we cannot fail to grasp the shockingly 

 fatal results that may accrue from an imperfect exami- 

 nation of a sample of water infected with the typhoid 

 bacterium. The fact was emphasized that infinitesimal 

 weights of bacteria cannot possibly be detected by the 

 aid of purely chemical methods, and that no examination 

 of water is complete unless it has passed through the 

 hands of an expert bacteriologist. One-sixtieth part of 

 crude sewage in 100 c. c. of distilled water gives a pro- 

 portion of about 1*7 of sewage per 10,000 of water. 

 Chemical analysis detects this small amount of organic 

 impurity, but the chemist looks upon this sample of 

 water as one of exceptional organic purity, and passes it 

 as a first-class potable water. But the bacteriologist has 

 methods at command which enables him to detect far 

 smaller proportions of organic matter, and he sees great 

 danger when water is contaminated with sewage to the 

 numerically small extent of one part in 500,000. 



The lecturer passed on to consider the conditions 

 that affect the growth and vitality of bacteria. All 

 bacteria may not be present in a given area in the same 

 proportion, and if a culture be made in a nutritive 

 medium that favors the growth of all alike, it is possible 

 to miss specific bacteria that may be of great importance. 



