IMMUNITY ANt> SUSCEPTIBILITY. 547 



chloric acid is diminished in amount, microorganisms may grow in the 

 stomach to a limited extent. Furthermore, in case all the particles of 

 food are not thoroughly broken up in the stomach, bacteria which may 

 be contained within these particles may pass through the stomach into 

 the intestine. 



The Intestines. In the intestines the microorganisms come in con- 

 tact with the alkaline pancreatic juice which is slightly antiseptic and 

 with the bile which is antiseptic and in certain instances bactericidal. 

 They find no particularly favorable conditions for growth in the upper 

 part of the small intestines under normal conditions. Here also mucus 

 covers the surfaces. However, if the functional activity of the small 

 intestines is disturbed, bacteria may enter the lymphatic structures 

 (Peyer's patches, solitary follicles) low down in the small intestines 

 and produce infection. Such is the case with B. typhosus, of typhoid 

 fever, and with the Msp. comma, of Asiatic cholera. Bacteria which 

 have been prevented from development in the small intestines frequently 

 find the opportunity in the large intestine. Here the reaction of the 

 various digestive juices is changed, the movements of contents slower, 

 and the requisite conditions for maximum bacterial growth are 

 provided. Nevertheless, infections of the large intestine with bacteria 

 are not common but may occur, colitis of various forms resulting. The 

 Amoeba dysenteries very frequently develops in the large intestine. 



Genito-urinary Tract. The mucous membranes of the genito-urinary 

 tract varying in male and female present the same features as those of 

 other mucous membranes. Besides the secretion of mucus, various 

 other acid-containing secretions are often present. In addition, in the 

 urinary tract the mechanical factor of irrigation removes the microorgan- 

 isms. Not infrequently, however, micoorganisms do enter these mucous 

 membranes and produce serious infections, such as the Treponema 

 pallidum, of syphilis, the M. gonorrhoea, and the B. chancr aides mattis. 

 Sometimes these membranes are infected with ordinary pyogenic bacteria. 



The Conjunctiva. The conjunctiva is protected against infection 

 in several ways. First, the eyebrows with their hairs and the eyelashes 

 prevent microorganisms and particles of dust and dirt-carrying micro- 

 organisms from entering the eye. Again, the tears flowing across the 

 eye from the outside in, serve to wash this membrane. Bacteria are fre- 

 quently washed off the conjunctiva and pass down through the lach- 

 rymal duct into the nose where they meet the obstructions which have 



