652 BACTERIA OF THE RESPIRATORY TRACT 



ities, and this appears to be true. For in the throat and the region above and below 

 the ileo-cecal valve, we find normally the greatest number and variety of bacteria, 

 as may readily be shown by making smear and culture preparations at intervals along 

 the respiratory and alimentary canal. In these two lymphatic maxima not only is 

 the normal bacterial flora more varied and numerous, but here occurs the greatest 

 number of infections: in the throat, streptococcus, pneumococcus, meningococcus, 

 staphylococcus infections, diphtheria, the viruses of numerous exanthemata, and 

 other diseases; in the lower intestine and colon, typhoid, paratyphoid, dysenteries, tu- 

 berculosis, appendicitis, etc. In the intervening localities relatively few infections oc- 

 cur. The pathogenic organisms often invade primarily the lymphoid structures them- 

 selves or the parts rich in lymphoid tissue. In other words, it would appear that, in 

 some instances at least, certain organisms become adapted to grow in lymphoid tissue; 

 that is, they attack the very mechanism which the body has apparently designed for 

 bacterial protection. Striking examples of this phenomenon are seen in the hemolytic 

 streptococcus infections of the tonsils. These are acute inflammations of these organs, 

 involving the surface and the crypts and are definitely contagious. Transmission is di- 

 rect, through droplets or contact. A variety of this infection is septic sore throat, many 

 epidemics of which now have been reported, where the tonsils are infected from drink- 

 ing milk containing streptococci that found their way there either from a person han- 

 dling the milk or from the cow whose udder had been infected and then served as an 

 incubator for these organisms. Experimentally, the writer showed some years ago 

 that cows might become carriers of these human hemolytic streptococci when injected 

 into the udder. These streptococci seem to have a very remarkable specific affinity 

 for the pharyngeal lymphoid tissue. 



The foregoing observations are quite in accord with a more or less general path- 

 ological principle which illustrates strikingly the adaptation that is taking place con- 

 tinually between our bodies and bacteria. The same principle is involved in the for- 

 mation by staphylococci and streptococci of specific substances called "leukocidins" 

 which destroy the defensive cells in our bodies, the leukocytes. Lymphoid tissue thus 

 may not be equally protective against all bacteria, and in certain infections this mech- 

 anism breaks down entirely and instead of being protective furnishes a fertile soil for 

 growth of bacteria and a route for invasion. The germs may directly attack this 

 tissue and successfully thrive there, at least for a time, until the body can marshal 

 defensive mechanisms of another order. It is on account of the prevalence of certain 

 infections in this tissue that it may be to the advantage of the body to remove this 

 mechanism or a part of it as is done in tonsillectomy, appendectomy, etc. 



The distribution of plasma cells in the body is suggestive in connection with in- 

 fections of lymphoid tissue especially of the respiratory tract. Generally speaking, 

 these cells are indicative of chronic inflammation or irritation, and most writers regard 

 them as pathological cells, at least when found in appreciable numbers. They accumu- 

 late in masses about centers of chronic inflammation and in general are characteristic 

 of granulation tissue. They appear in many low-grade inflammations of the skin and 

 mucous membranes. 



Using the local accumulation of plasma cells as a possible criterion of the ab- 

 sorption of bacteria or their products, the writer studied the time of appearance and 



