34 Proceedings of the Royal Physical Society. 
_ 2. Potato—On the cut surface of a sterilised potato the 
bacilli grow well, but on looking at the surface of such a 
potato nothing unusual is observed, at least on a cursory 
examination of the inoculated surface. On more careful 
examination, however, a thin almost transparent “skin” can 
be made out, and the smallest portion of this “skin” or pelicle 
on microscopic examination reveals the presence of a large 
number of little rods or bacilli with rounded ends. When 
the bacilli are examined under suitable conditions, they are 
found to be exceedingly motile, and not only are they motile, 
but they are exceedingly variable in length, and some are 
even so reduced in length as to resemble small spheres or 
micrococcl. 
Before considering the various modes of isolating the 
typhoid bacillus from contaminated water and milk, let me 
briefly call your attention to the various ways in which this 
contamination is brought about. 
A. The Contamination of Water—1. Through the medium 
of the air: (a) from “sewer gas” containing the germs of 
typhoid fever coming in contact with drinking water; (0) 
from noxious emanations from typhoid excreta in cesspools, 
on soiled linen, etc. It is important to note, in connection 
with emanations from typhoid excreta (as is the case with 
Asiatic cholera), that freshly passed excreta are not nearly 
so dangerous as excreta which have been exposed for some 
time to the air. 
2. Through excreta getting directly into the drinking 
water. This has been a fruitful source of typhoid outbreaks. 
At the present moment an experiment on a large scale is 
being carried out across the border. I refer to the river 
Tees in England, into which the excreta from several of the 
villages along its banks find their way into its waters; also 
used for drinking purposes, with the consequence that typhoid 
fever is more or less prevalent along the valley of the Tees, 
breaking out every now and then—especially after heavy 
rainfalls—into severe and fatal epidemics. 
3. Through an attendant on the sick. The question 
whether a person, himself unaffected, but who has been in 
attendance on a typhoid patient, may contaminate water, 
