i66 PRACTICAL BACTERIOLOGY. 



■which were originally present in the distilled water 

 have, after eight days, multiplied considerably, those 

 which were introduced have, on the contrary, decreased 

 in number, having been starved for want of suitable 

 nourishment. 



Thus, since great numbers of these putrefaction 

 bacteria cannot exist in pure watei', it is evident that 

 a water which harbours many colonies of bacteria 

 which liquefy. the gelatine, must have been not only 

 contaminated through the addition of filthy water, but 

 must also have been so rich itself in organic nutrient 

 substances, that the putrefaction bacteria are able to 

 live in it. 



Hence, if we wish to examine a sample in order to 

 discover its bacteriological contents, we must take 

 into account the number of the colonies, the number 

 of the species, and the characteristics of these species. 

 No great importance is to be attached to the number 

 of colonies, as has been shown ; on the other hand, 

 water which contains a great many different kinds, 

 amongst which are several which liquefy the gelatine, 

 must be condemned as unfit for drinking purposes, 

 even if the chemical analysis has been satisfactory. 

 The question now arises, How many kinds may be 

 allowed in drinking water ? 



It is evident at the outset that a hard and fast line 

 cannot be drawn, and that our opinion must be based 

 upon the consideration of all the facts. Above all we 



