PORTALS OF ENTRY OF INFECTIOUS AGENTS. 169 



but also to fumigate clothing, bedding, and even letters, 

 that had been in most casual contact with the sick. 

 The measures enforced indicate that the causative 

 agent was believed capable of gaining an entrance into 

 the body without injury to the skin or mucous mem- 

 branes. We now know, however, that a lesion of the 

 skin inflicted by a mosquito is its only means of entrance 

 (although we are yet in the dark as to the nature of the 

 agent), and that, therefore, all former methods of pre- 

 vention were futile in so far as control of the disease was 

 concerned. Into such gross errors is it possible to 

 fall when we apply methods of proven value in known 

 to unknown diseases! Another case in point: Take 

 typhoid fever; the typhoid bacillus enters the body by 

 the mouth in food or drink. The most obvious lesions 

 of the disease are seen in ulcers of the lymph nodes 

 (glands) of the lower part of the small and the beginning 

 of the large intestines. To affect these results the 

 bacilli pass through the mucous membrane of the 

 bowels, where they can be seen with the microscope in 

 stained sections after death. The specific bacilli, 

 however, do not stop in the sub-mucosa (sub-mucous 

 tissue) but pass from here into the blood, where active 

 growth and toxin formation is carried on. In other 

 words, typhoid fever belongs to the bacteriaemias, a 

 class of diseases characterized, as we have seen, by the 

 presence of bacteria in the blood. Usually the more 

 obvious symptoms of typhoid fever are those referable 



