PORTALS OF ENTRY OF INFECTIOUS AGENTS. 179 



it is a wise precaution to suspect the drinking-water. 

 But where cases are reported sporadically, especially 

 in communities which have a municipal water system, 

 it is more logical to seek the source elsewhere. The 

 modern method of food distribution is a marvelous 

 development, that is comparable to other inventions of 

 the 19th Century. Through it perishable articles are 

 not only distributed from one point where the supply 

 exceeds the demand to others where they are needed; 

 but they are also held, in the case of certain foods, a 

 year or more — if the supply is too abundant. Nor is 

 the distribution of such things limited to the farther- 

 most boundaries of one country, but they are also 

 shipped from one country to another across the widest 

 seas. All this has come about through the expansion 

 of the cold storage business, and the use of refrigerator 

 cars, and cold storage plants on steam-ships. There 

 is a large and ever increasing demand for various perish- 

 able articles of food out of season, so that there is a 

 constant movement of supplies from one region to 

 another. Furthermore, this demand has stimulated 

 the speculative zeal of those engaged in the cold storage 

 business, with the result that ''in season" enormous 

 storing of perishable foods is conducted. So great at 

 these times is the demand for these commodities for 

 storage, and for shipment to other parts of the country, 

 that in many localities where they are grown it is im- 

 possible to purchase in the local market either fresh 



