12 THE POPULAR SCIENCE MONTHLY
cooked foods which have been improperly handled in the kitchen, rather than to original infection of the meat before it enters the house- hold.
Of the food materials which are eaten raw and might therefore be expected to play an important part in the wholesale transmission of disease, some, like certain fruits, are rendered safe by the fact that they are peeled before being eaten so that the edible portion has never been exposed to infection. Others are protected by the fact that long storage usually intervenes between exposure to pollution and ultimate consump- tion. Thus ice, though often cut on polluted streams, is one of the safest foods, as shown by careful bacteriological and epidemiological studies. Ninety per cent, of the bacteria in the water are thrown out in the physical process of freezing ; and in a few weeks ninety-nine per cent, of any disease germs remaining will have perished.
Water and milk and raw shellfish are the three foods which in the highest degree fulfill all the requirements of a dangerous disease medium. If water is taken from streams or ponds or wells into which sewage enters, and is used for drinking without adequate storage or purification, the best possible opportunity is offered for a transfer of infection on a gigantic scale. The great epidemics of typhoid fever and cholera which used to sweep through European cities and more recently have continued to ravage American communities, bear eloquent testimony to this fact. With the cheap and effective methods of puri- fying water, by storage, filtration or disinfection, now at our disposal, there is no excuse for the delivery of a public water supply which is not absolutely safe. In uncivilized communities, which persist in using polluted supplies, and in the country where a local well is under sus- picion, the householder may always, however, protect himself by using a Berkefeld or Pasteur filter, either of which types is efficient if prop- erly cared for, or by boiling the water to be used for drinking.
Milk is second only to water as an agent in the transmission of dis- ease. It is frequently infected with tubercle germs and sometimes with other pathogenic organisms from the cow. It is contaminated by dirt in the stable, and it is polluted at a dozen different points by the numerous individuals who handle it on its way through the dairy to the consumer. Furthermore, of all foods milk is the one which in some cases apparently permits an actual multiplication of disease germs and an increase in- stead of a diminution of virulence in transit. Epidemics of typhoid fever, diphtheria, scarlet fever and tonsilitis without number have been traced to milk, and to young children even the ordinary germs of decay in milk, aside from infection with specific diseases, are often fatal, as evidenced by the terrible toll of summer diarrhoea among infants, which is almost exclusively confined to those fed on cow's milk. Carefully protected milk, such as is certified by our medical societies, is of course much freer from danger than the ordinary product, but the history of