yc IMMUNITY IN HEALTH 



small part in the production of the lymphocytosis, 

 surely a defensive reaction. In connection with the 

 greater activity of the lymphatic tissues in children, 

 it is worth while repeating that a lymphocytosis is more 

 easily provoked in early life, and that the lymphocytes 

 form a constantly higher proportion of the leucocytes 

 in children than they do in the adult. 



Further, it has already been shown (Chapter V.) that 

 during scarlatinal epidemics a person may apparently 

 secure immunity by a very mild tonsilitis, which is un- 

 accompanied by rash, malaise or other signs of general 

 injury, and that a similar immunity may be obtained 

 in epidemic cerebro-spinal meningitis. A great pro- 

 portion of those exposed to infection show the virus 

 on their nasopharyngeal tonsils (which are liable to 

 show some congestion), yet remain free from the disease 

 and have indeed developed an enormously high opsonic 

 index against the causal micro-organism. 



Similarly, immune " carriers," who have never clini- 

 cally suffered from the diseases, yet convey the organ- 

 isms of typhoid and cerebro-spinal fever and of 

 diphtheria, cholera and dysentery (Ledingham and 

 Ark Wright). 



In France, Courmont and Rochaix have produced 

 immunity against typhoid fever both in human beings 

 and animals by the introduction of dead bacilli into 

 the large intestine. Agglutinins have resulted in the 

 blood stream. It seems likely that the dead organisms 

 pass through the epithelium into the subjacent lymph 

 nodes of the solitary follicles or the appendix — just as 

 living organisms do — and that the immunity is pro- 

 duced in that manner. 



Finally attention may again be drawn to the patho- 

 genic organisms normally inhabiting the alimentary 

 canal. It would be difficult to understand how pneumo- 

 cocci, Klebs-Loffler Bacilli, and the hosts of pyogenic 



