METHODS AND CHANNELS OF INFECTION. 537 



influenza, pneumonia and tuberculosis from the bronchial membranes; 

 diphtheria, leprosy, glanders and scarlet fever from the membranes 

 of the nose, throat and tonsils; and gonorrhoea, syphilis and tuberculosis 

 from the membranes of the genito-urinary tract. In elimination from 

 the various internal membranes sometimes re-infections occur such as in 

 the case of the elimination of Bact. tuberculosis from the respiratory tract, 

 the swallowing of the sputum, and the subsequent infection of the 

 intestines. 



In the second, or indirect method of elimination, two distinct proposi- 

 tions present themselves: first, the infectious microorganism must 

 enter the lymphatic or blood circulation and, second, in order to get 

 out of the body they must pass through the cells of some of the organs, 

 the mucus membranes or skin. It is a common occurrence for bacteria 

 and other microorganisms to get into the circulation in some of the 

 infectious diseases such as typhoid fever, pneumonia, plague and in the 

 various septicaemias. They may pass through the epithelium of the 

 kidney and be eliminated in the urine; they may pass through the liver 

 and be eliminated in the bile, passing out through the intestines; they 

 may pass through the mucous membranes of the intestine and possibly 

 pass through the glandular epithelium of the sebaceous and sweat glands 

 and be eliminated through the skin. They have also been known to 

 migrate through the glandular epithelium of the milk glands when these 

 glands are not grossly diseased and also through the salivary glands. 

 Infectious microorganisms are sometimes destroyed by the lysins in the 

 blood, carried to and deposited in the spleen and bone-marrow and 

 gradually disintegrated and dissolved. 



In certain infections in which a recovery seems to have occurred, 

 all the pathogenic microorganisms have not been eliminated from the 

 body. As mentioned previously, B. typhosus and Bact. diphtheria are 

 frequently carried by persons fully recovered from these diseases. 

 Sometimes, however, inflammatory infections are set up by these bac- 

 teria. It is suspected that frequently repeated attacks of malaria are 

 due to the retention of some of these protozoan parasites which for a 

 time exist in a quiescent stage. Repeated attacks of erysipelas caused 

 by the Strept. pyogenes may also be due to the same condition. It is 

 claimed also by some (von Behring) that Bact. tuberculosis is taken into 

 the body in infancy, that it is not eliminated, and that it sets up infection 

 in later life. 



