74 MICRO-ORGANISMS AND DISEASE [chap. 



crements included— such water should, on Koch's standard, 

 not contain above loo bacteria per i cubic centimetre. 

 I had the opportunity of examining these waters (eight 

 companies) for eight consecutive weeks, and found that out 

 of sixty-four samples thus examined only in eight were the 

 number one hundred or below, in the others above, in a 

 majority as numerous as in the unfiltered raw water. 



The plate-cultivations thus made for ascertaining the 

 number of bacteria can be used for a superficial estimation 

 and the study of the character of the microbes, but it must 

 be understood that having used for each plate only a very 

 small quantity of the water, a fraction, say, of one to two 

 cubic centimetres, only those microbes will be met with in 

 these plates which occur in large numbers ; as to those that are 

 distributed in the water as a whole in hmited numbers, there 

 is little chance of meeting them in a couple of plates inocu- 

 lated with only 1-2 cc. of the water. The bacteria almost 

 constantly present in small quantities, leaving out yeast and 

 fungi, are : — {a) bacillus fluorescens liquescens, easily recog- 

 nised by the rapid liquefaction and greenish tint of the 

 liquefied parts ; (p) bacillus sulcatus, in several varieties, not 

 liquefying, white, rounded, flat moist colonies ; {c) micrococ- 

 cus, liquefying and non-liquefying ; {d) not infrequently one 

 or the other variety of bacillus mesentericus, motile large 

 bacilli, liquefying slower than fluorescens. The most im- 

 portant part of the examination refers to the detection of 

 microbes which are present in putrefying animal matter, 

 notably in sewage or animal excrements, or are derived from 

 the diseased bowels of man. Amongst these are bacillus coli, 

 proteus vulgaris, proteus Zenker!, or a variety of it, and 

 above all bacillus of typhoid and vibrio of cholera. 



