48 WATER 



bacilli are absent and the supply in its present condition a safe 

 one. 



Viability of B. typhosus in water. 



The viability of the typhoid bacillus in water has been made 

 the subject of many investigations. Only a few of the more 

 recent and extended can be mentioned here. 



The results of many of the investigations are conflicting. In 

 explanation of the discrepancies several points may be urged. In 

 the first place, many of the experiments have been carried out 

 under highly artificial conditions. For example, the bacilli have 

 been added to water small in bulk and kept confined in vessels, 

 such as in flasks or bottles. Typhoid bacilli in such circum- 

 stances are not under conditions of light, movement and compe- 

 tition with naturally occurring bacilli such as must take place 

 under natural conditions. Deductions from such experiments 

 furnish no real guide as to the viability of the typhoid bacillus 

 under actual practical conditions of pollution of a water supply 

 by material containing this bacillus. When water supplies are 

 contaminated with typhoid bacilli the vehicle of infection is 

 usually the urine or faeces of cases. Such material generally 

 contains vast numbers of other bacilli. It is also probable that 

 the viability of any added bacilli is considerably influenced by 

 the addition of the considerable amount of organic matter which 

 usually in this way gains access to the water. 



A further factor of undoubted importance is the individual 

 resistance of the bacilli added to the water. Many of the earlier 

 .experiments were conducted with typhoid bacilli which had been 

 cultivated in the laboratory outside the animal body for long 

 periods. Houston 1 found that typhoid bacilli direct from the 

 animal organism died much more rapidly in river water than strains 

 previously cultivated in the laboratory. In 13 experiments with 

 the "uncultivated" typhoid bacilli the bacilli could not be found 

 in the infected water after one week (9 experiments), after two 

 weeks (3 experiments) and after three weeks (i experiment): 

 yet the same microbe after " cultivation " usually lived over five 

 weeks. 



1 Seventh Research Report, p. 3. 



