MAN AND THE MICROBE n 



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 infec- 

 tious 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 allitera- 

 tively 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 



