﻿NO. 8 RECOVERY FROM INFECTION FLEXNER 5 



The injection of microorganisms into the blood by insects is a more 

 subtile means of causing infection, and it is not only established be- 

 yond peradventure, but is of the highest possible significance. It 

 may be stated that this discovery, as much as any other in the whole 

 realm of preventive medicine, has determined the methods, already 

 successfully invoked in many countries, of suppressing highly fatal 

 forms of disease. The range of parasitic causes of disease known to 

 be thus inoculated, as well as the insects that inoculate them, is 

 wide. Mosquitoes carry malaria and yellow fever ; biting flies carry 

 trypanosome infections, including the deadly sleeping-sickness; ticks 

 and bed-bugs carry spirochetal infections, including the severe and 

 fatal African tick fever and relapsing fever; body lice carry typhus 

 fever ; and fleas carry plague. This list includes all classes of para- 

 sitic microorganisms. The protozoa are represented by the malarial 

 parasites and trypanosomes, the bacteria by the plague bacilli, and 

 the submicroscopic organisms by the cause of yellow fever. 



Still other factors contribute to determine infection. The period 

 of childhood is especially characterized by a class of infections that 

 depend upon imperfections in the anatomical barriers that are far 

 more adequate in adult life. Many of the diseases that we associate 

 with childhood — measles, scarlet fever, diphtheria, epidemic menin- 

 gitis, and poliomyelitis, already mentioned — utilize the mucous 

 membranes of the nose and throat to gain a foothold in the body, 

 because they are notably vulnerable. Their crypts or depressions 

 afford a lodging place in which multiplication of the parasites can be 

 effected, and the breaks in the epithelial covering constitute the first 

 breach in the external defenses which the parasites seek to and suc- 

 cessfully do enlarge. Tuberculosis of the lymphatic glands of the 

 neck and of the bronchi occurs especially in the young, and also, 

 because of the greater permeability of the corresponding mucous 

 membranes, in children. The intestinal mucous membrane also is 

 permeable to a greater degree for microbes in the young, and thus 

 they are exposed far more than are adults to food infection with the 

 tubercle bacillus. Moreover, the whole group of microbic infections of 

 the stomach and intestines of children, which creates such sad havoc 

 during the warm summer months, depends upon two things ; smaller 

 power of excluding germs by their mucous membranes, and a variety 

 of food that is a highly perfect medium for varied microbic growth. 

 In older persons, the incidence of typhoid fever ceases with the 

 anatomical changes coming in the fourth decade of life, that reduce 

 the absorbing power of the intestine for bacteria ; while certain par- 



