CONTROL OF BACTERIAL DISEASES 237 



by angry gods, demons, and witches; next, by the air as 

 r liasms and effluvia ; then, by fomites in dust of clothing or 

 Merchandise; and, finally, we have come down to the sure 

 evidence of science that contact infection, chiefly by the 

 hands, accounts for almost all the spread of common diseases, 

 tind insects, by contact or inoculation, for most of the rest. 



Air not an important carrier. Just now the air is rapidly 

 losing all its terrors, smallpox being the only disease which 

 may possibly, though not probably, be carried from house to 

 house by this agency. (This does not mean that insects that 

 :ly may not transmit many infections by contact.) Chapin 

 puts the case carefully and sensibly as follows : 



Only a few authorities now assert that disease is carried by the 

 itmosphere outside of dwellings, and this assertion is made only in 

 regard to smallpox. . . . Infection by air, if it does take place, as is 

 ommonly believed, is so difficult to avoid or guard against, and so 

 universal in its action, that it discourages effort to avoid other sources 

 of danger. If the sick-room is filled with floating contagium, of what 

 use is it to make much of an effort to guard against contact infection? 

 If it should prove, as I firmly believe, that contact infection is the chief 

 way in which the contagious diseases spread, an exaggerated idea of 

 the importance of air-borne infection is most mischievous. It is impos- 

 sible, as I know from experience, to teach people to avoid contact in- 

 fection while they are firmly convinced that the air is the chief vehicle 

 of infection. . . . Without denying the possibility of such infection, it 

 may be fairly affirmed that there is no evidence that it is an appreciable 

 factor in the maintenance of most of our common contagious diseases. 

 We are warranted, then, in discarding it as a working hypothesis and 

 devoting our chief attention to the prevention of contact infection. It 

 will be a great relief to most persons to be freed from the specter of 

 infected air a specter which has pursued the race from the time of 

 Hippocrates; and we may rest assured that if people can as a conse- 

 quence be better taught to practice strict personal cleanliness, they 

 will be led to do that which will, more than anything else, prevent 

 aerial infection also, if that should in the end be proved to be of 

 more importance than now appears. CHAPIN, "Sources and Modes 

 of Infection," p. 20o ff, 



