THE TRANSMISSION OF INFECTIOUS DISEASES 55 



is conveyed to man by the rat, through the medium of 

 fleas which infest these animals. A few years ago it 

 would have been difficult to find a text-book which did 

 not in positive terms state that typhus fever is trans- 

 mitted by clothing, baggage, and other articles. Yet 

 careful investigations, particularly the recent work of 

 Goldberger and Anderson in Mexico, proves that the 

 disease is transmitted by the body louse and not by 

 fomites. With regard to two common diseases of child- 

 hood, namely, measles and scarlet fever, public health 

 authorities are coming more and more to believe that 

 desquamation of the skin is a negligible factor, and that 

 these diseases are conveyed from person to person by the 

 infected discharge of the mucous membrane involved. 



It is only within comparatively recent years that we 

 have appreciated the importance and danger of mild, 

 ambulant, or irregular cases of infectious diseases, and 

 the frequency with which they occur. They are un- 

 doubtedly one of the most common and dangerous fac- 

 tors in the transmission of infection because they often 

 pass unrecognized. More recently we have learned of 

 "carriers," or persons who, while themselves well, 

 harbor the specific micro-organism, and may transmit 

 it to others. These undoubtedly play an important 

 role in the spread of infectious diseases. 



All these observations have served to discredit the 

 fomites theory, and, while there is no doubt that in some 

 rare instances clothing, rags, books and toys, etc., may 

 act as a medium of infection, we should devote our at- 

 tention principally to the usual or common means of 

 infection. The knowledge we now possess on this sub- 

 ject proves that infectious diseases are transmitted by 



