104 IMMUNITY IN HEALTH 



creased : bacteriolysins and antitoxins are produced in 

 large quantities. The subepithelial lymphatic glands 

 confer upon their owners some immunity against the 

 alien myriads of bacteria. They are the immunising 

 stations, or, if you like, the auto-vaccination organs of 

 the body. 



The line of argument leading to this hypothesis can 

 in brief be indicated thus. The subepithelial lymphatic 

 glands have appeared, reached a high stage of develop- 

 ment and persisted throughout the two highest classes 

 of animals — namely birds and mammals. And this in 

 spite of the apparent anomaly of their great liability 

 to serious infectious disease. They must have a com- 

 pensating function of great value. The continuous in- 

 gestion of bacteria by the subepithelial lympiiatic 

 glands considered together with our knowledge of 

 healthily acquired immunity to infectious disease sug- 

 gests the hypothesis of their auto-vaccinating function. 



The chief points in favour of the hypothesis may be 

 summarised below : — 

 Biological : — 



(1) The subepithelial lymphatic glands are only pre- 

 sent in the two latest, highest and most successful 

 classes of animals — namely birds and mammals. 



They occur without exception throughout these two 

 classes, including phyla of considerable antiquity in a 

 geological scale. 



Organs of no value become suppressed over long 

 periods of time (Chapter XIX.). As the subepithelial 

 glands are often the seat of disease, their suppression 

 would have been accomplished long ago, had they not 

 some compensating functions of great value. 



(2) With regard to the mammalian caecum, lymphoid 

 tissue is almost universally present. Sometimes this 

 forms a protuberant mass at the apex. Quite frequently 

 and in many widely different phyla the lumen of the 



