I70 INFECTIOUS AND PARASITIC DISEASES. 



to the bowels; but the intestinal features may be com- 

 pletely wanting, as has been repeatedly proven by post 

 mortem examinations. Such cases are usually reported 

 as ^^ Typhoid fever without intestinal lesions." A 

 study of typhoid fever, therefore, teaches that, while 

 the agents of a disease may depend for entrance into 

 the blood upon a gross or macroscopic lesion of a 

 mucous membrane, they also may enter through a non- 

 demonstrable portal. It might be asked at this point, 

 ^^why do not the bacteria which get into the intestinal 

 tract with food, and those which have their habitat there, 

 often penetrate the mucosa and cause disease?" The 

 answer to which would be, they do, far oftener than is 

 generally supposed; in fact the intestinal tract is re- 

 garded as the chief portal of entry for many diseases 

 for which no atria can be found (cryptogenic infections). 

 That some bacteria can enter certain tissues and 

 attack certain localities more readily than others is 

 admitted, because it has been experimentally proven. 

 But between experiments, no matter how cunningly 

 devised, and disease, as ordinarily contracted, there is a 

 wide gap. When an animal or person is subjected to 

 the germs of a disease, many million times the number 

 of bacteria are applied than are ever present under 

 natural conditions. Under such circumstances mere 

 contact of these germs with the right mucous surface is 

 sufficient to provoke disease. This is the case, for 

 example, with the diphtheria bacillus, accidental infec- 



