152 PRACTICAL BACTERIOLOGY. 



opinion formed of its hygienic^ properties ; that is to 

 say, we may discover by these means if the water is 

 capable of harbouring typhoid bacilli. 



It is next necessary to make clear to ourselves how 

 the typhoid bacillus spreads. Although it is not one 

 of those bacteria which can develop only in the 

 animal body, but is capable under certain circum- 

 stances of developing even in our climate outside of 

 the body, yet this very rarely occurs, especially as the 

 bacilli are exceedingly liable to be overwhelmed and 

 completely covered over with a luxuriant growth of 

 saprophytic bacteria. On this account only sporadic 

 cases of typhoid can be ascribed to these "free-living" 

 bacteria, if we may so use the term. Should however 

 one such first case of typhoid occur in a neighbour- 

 hood, there is a possibility that a greater or smaller 

 epidemic may ensue in consequence. Typhoid bacilli 

 pass out exclusively with the excrements of infected 

 persons, and if these are not disinfected, but are cast, 

 containing, as they frequently do, great quantities of 

 the bacilli, into cesspools or down drains, the fetters 

 with which the pestilence might have been bound 

 have escaped from the hand of man. Several different 

 contingencies may occur ; the typhoid bacilli may be 

 carried away in different directions, generally impos- 

 sible to trace. If the opportunity is afforded us of 

 examining carefully a number of farm-yards in the 

 country, we find that in a great number of cases it 



