68 IMMUNITY IN HEALTH 



are such as to encourage stagnation of the alimentary 

 contents, and stagnation in its turn will tend to the 

 multiplication of bacteria and their toxins. 



In the lumen of the alimentary canal then are found 

 man}^ millions of bacteria; on the other side of the 

 epithelium in the lymphoid tissue are to be seen fewer 

 millions of similar bacteria. The question arises by 

 what means these bacteria have been translated across 

 the epithelium. What is the mode of ingestion of these 

 bacteria by the subepithelial lymphatic glands ? 



Four possibilities readily occur to one. These hypo- 

 thetical processes may be termed : — 



1. Chemiotaxis. 



2. Physiotaxis. 



3. Bacterial motility. 



4. Phago taxis. 



1. Chemiotaxis, — It is known that phagocytes ap- 

 proach bacteria. If the phagocyte is enmeshed in 

 retiform tissue the bacteria might conceivably be 

 attracted to the phagocyte by chemical means. 



2. Physiotaxis. — Alterations of surface tension 

 might determine the passage of bacteria between the 

 epithelial cells. 



3. Bacterial Motility. — The powers of locomotion 

 possessed by many bacteria might lead them through 

 the epithelial wall into the lymphoid tissue. This per- 

 haps would be the view of those who regard the 

 subepithelial lymphatic glands simply as weak spots 

 poorly able to resist bacterial assault. 



4. Phai^o taxis. — It is common physiological know- 

 ledge that lymphocytes leave the subepithelial 

 lymphatic glands, passing between the epithelial cells 

 into the lumen of the alimentary canal and there 

 engulf bacteria. Ruffer, in 1890, examined the mucus 

 from the surface of human tonsils in four normal 

 persons, and in each case met with "many leucocytes 



