quiet indoor air contains comparatively few microbes of any kind and is singularly free from germs of human origin. So strong is the evidence of the insignificance of aerial infection that in some of the most modern hospitals, cases of various contagious diseases have been treated with perfect success in open wards, provided, of course, that the most rigid precaution be taken to prevent the direct transfer of infectious material by the hands and clothing of attendants.
One of the most striking examples of the exorcism of a bogey of the older sanitation by modern exact methods is the case of sewer gas. Dreaded as a prime spreader of disease ever since sewerage began, we now know that sewer and drain air is freer from microbes than the air of a city street, and that the microbes which are present are of the same harmless type in the two cases. From a careful series of experiments in Boston, it was calculated that if one placed the mouth over a house drain and breathed the drain air continuously for twenty-four hours the number of intestinal microbes ingested would be less than those taken in in drinking a quart of New York water, as it was before routine disinfection of the supply was introduced.
Disease germs do not enter the household through the sewer pipes or by flying in at the windows (unless borne on the wings of insects). They are not to any important extent brought in on books or toys or clothing, where, if any infection existed, it has mostly dried up and died. They are brought in directly by infected persons (carriers). They are brought in by insects. They are brought in by certain articles of food and drink. These three types of transmission, which have been alliteratively described as infection by fingers, flies and food, account for ninety nine cases of communicable diseases out of a hundred, and each of them deserves a somewhat more detailed consideration.
In order that a given food may be important as an agent in the transmission of disease there are three different conditions which must be met, and it is only in a few instances that all three are met at once. The substance must be exposed to infection, it must be delivered and used promptly and it must be eaten raw. For the great majority of our foods cookery furnishes an effective safeguard and, as has been often pointed out, the sanitary results of this practise must have played an important part in the evolution of the human race. Most processes of cookery destroy the disease germs and their toxins and make it possible to use such foods as the meat from slightly tuberculous animals with entire safety. It is fortunate that this is the case because the ideally healthy animal is as rare as the perfect human being, and the increasing burden of the cost of living makes it essential that we should utilize all food materials which can be consumed with safety. The common practise, in certain European countries, of eating meat only partially cooked often leads there to serious epidemics of meat poisoning, but in America such outbreaks are usually due to subsequent infection of
