62 



THE AMERICAN MONTHLY 



[April, 



contain living forms, both animal and 

 vegetable. When collected in test tubes 

 or stoppered bottles, these forms of 

 life usually perish, and then become 

 the prey of iDacteria, which feed upon 

 their dead bodies and multiply. 

 Standing water therefore becomes an 

 organic infusion comparable to artifi- 

 cial culture liquids. 



It is therefore essential that water 

 be examined immediately after it is 

 collected, or else placed in conditions 

 which will pi-event the multiplication 

 of the bacteria. The collecting tubes 

 should be placed upon ice, or kept at 

 a temperature at least below 50° F. 



The relation of minute vegetable 

 and animal forms, such as unicel- 

 lular and higher algaj, rhizopods 

 and infusoria, to the healthfulness of 

 water is still a matter of conjecture. 

 It is w^ell known that the richest 

 microscopic fauna and flora are to 

 be found in standing and very slowly 

 flowing waters, while in fresh water 

 from springs there is very little life 

 of any kind. According to Magnus* 

 the presence of algie is not detrimental 

 to the quality of drinking water pro- 

 vided the volume of water is at no 

 time diminished to such an extent as 

 to cause the death of these algie and 

 thus furnish food for bacteria. 



The eftect upon water of a pro- 

 longed stay in reservoirs needs also 

 careful examination. The algte 

 wdiich require sunlight, and probably 

 some animal forms which live in 

 flowing streams, when suddenly 

 brought into deep reservoirs may die 

 and furnish food for bacteria. At 

 the same time this bacterial vegeta- 

 tion may thrive only on the bottom 

 where the organic debris subsides, 

 and if the temperature be low bac- 

 terial multiplication maybe retarded. 

 These factors will counteract each 

 other more or less so that it is diffi- 

 cult at present to state definitely how 

 flowing water is aflecfed when, col- 

 lected in reservoirs until comparative 

 experiments have been made. 



There are two reasons why waters 



*\Volffhugel: Wasservcrsorgung, 1882. S. 131. 



containing a lai'ge nvmiber of bacteria 

 should be looked upon with suspi- 

 cion : I. The source of the bacteria 

 may, at some time, prove a source of 

 disease germs, since bacteria in 

 general come from decomposing 

 organic matter. 2. Waters which are 

 able to support a large number of bac- 

 teria may be able to sustain pathogenic 

 bacteria. The latter may even mul- 

 tiply in the water before it is con- 

 sumed. 



It is now generally believed that 

 the specific microbes which are the 

 cause of cholera and typhoid fever, 

 and we may add some of the milder 

 forms of intestinal disturbances, are 

 usually introduced into the system in 

 the water consumed. It is not un- 

 reasonable to suppose moreover that 

 drinking water may be the vehicle of 

 other diseases under exceptional cir- 

 cumstances. From this it follow'S 

 that the water supply of communi- 

 ties should be under constant, careful 

 observation and that any changes in 

 its cpiality from time to time should 

 be noted and investigated, and that 

 the best methods of purifying and 

 filtering should be employed before 

 it is distributed for c<Misumption. 



The final test in the biological ex- 

 amination of water consists in the 

 actual demonstration of disease germs 

 in the water. Here we meet with 

 great difficulties. In the first place it 

 is highly improbable that even a bad 

 water contains disease germs, except- 

 ing in times of epidemics. In the 

 second place, most of the disease 

 germs with which w^e are acquainted 

 grow very poorly, or entirely fail to 

 develop on gelatin. And nearly all 

 disease germs multiply tar more 

 slowly than the putrefactive bacteria 

 among which they grow and by 

 which they are soon overgrown. 

 Thus the bacillus of tuberculosis 

 grows only at the temperature of the 

 body, andhence would not appear in 

 the gelatin layer, assuming that its 

 spores are present. 



There is, however, another class of 

 microbes not yet fully understood, 



