100 IMMUNITY IN HEALTH 



here — that they are constantly sampling adjacent 

 bacteria and immunising the body against their in- 

 vasion. Considering that they are constantly engulfing 

 bacteria, it is seen how relatively infrequent is their 

 defeat. An occasional attack of tonsilitis or appendi- 

 citis indeed may well be a cheap ransom to pay for 

 immunity from general infections of far greater fre- 

 quency and severity. 



That the balance of the action of these subepithelial 

 lymphatic glands is advantageous is indicated by their 

 occurrence in the height of their development in the 

 later, more developed and more successful types of 

 animals. 



The simple forms of subepithelial lymphatic glands 

 merely underlie the epithelium ; in the more complex 

 types some kind of cul-de-sac arrangement is seen, for 

 instance the blind lumen of the vermiform process or 

 the lacunae of the tonsils. The stagnation which results 

 may perhaps favour bacterial growth in close vicinity 

 to the lymph nodules and in some cases the cul-de-sac 

 arrangement may lead to some control over the ex- 

 posure to this growth. Thus the vermiform process 

 may be likened to a test-tube which is filled at intervals 

 with samples of the caecal brew and which can be 

 emptied by the contractions of its own musculature 

 and washed by the mucus of its own secretion. 



The cul-de-sac arrangement has this weakness that 

 stenosis or blockage of the lumen of the cul-de-sac 

 which may follow one attack of inflammation, will pre- 

 dispose t'o a recurrence of the trouble. 



Where the subepithelial lymphatic gland is sur- 

 rounded outside by a strong protecting capsule (as for 

 instance the faucial tonsil tying in its fibro-muscular 

 bed), if suppuration occurs its spread is limited. But 

 hyperplasia from excessive work causes an enlargement 

 towards the alimentary lumen and mechanical ill- 



