TEST FOR TYPHOID BACILLUS IO7 



ings are often wholly negative, because of the long incubation 

 period (14 days), so that the bacilli may all have disappeared 

 from the sewage or water between the time of the infection and 

 the manifestation of the symptoms of the disease. Under con- 

 ditions favorable to the typhoid germs, as food supply, temperature, 

 absence of sunlight, etc., they may survive for several months. 

 It is generally conceded that the Bacillus typhosus is quite re- 

 sistent and persistent. According to Ravenel, the germ survives 

 for several months and longer in fecal matter deposited in snow 

 which when carried into the stream supplying a 

 city with drinking water by the early spring 

 rains caused an outbreak of typhoid. 



The highly objectionable method of using 

 human excrement for fertilizing the soils of 

 truck gardens, as practised by the Chinese and 

 others, may lead to the typhoid contamination Fig "7,2 — lUus- 



of the vegetables grown in such gardens. Wash- trating the Widal 

 ings of the soil and of the vegetables should be nomenon. Upper 



examined for typhoid germs. J^.^'f before the reac- 



' ^ ° 1-1 tion. Lower half 



The following general method for the isola- shows clumping of 



tion of the typhoid bacillus is suggested, subject lilJ^'^ufiM.) ^''''~ 

 to modification to suit special cases. 



1. Concentration. — Run from i to 10, and more, liters of 

 water (as from well, cistern, stream, water tank, etc.) through a 

 clay filter. Just before all of the water has passed through the 

 filter, shake it up and pour into a suitable centrifugal tube (the 

 special tube already described will answer the purpose very well) 

 and place in incubator for 30 min. at a temperature of 37° C. 

 The incubating is done for the purpose of increasing the motility 

 of the typhoid bacilH. 



2. Separation by Centrifugalization. — Take tube from the 

 incubator and centrifugalize for from 5 to 30 min. at a high speed. 

 The non-motile bacteria will be thrown down first, while the 



