106 INFECTION AND IMMUNITY. 



leucocytes ( ! ) ,and within similar cells which were 

 found in the liver and spleen (Adami's Principles 

 of Pathology, Vol. I, p. 291). Inasmuch as no 

 power of spontaneous penetration can be ascribed 

 to the particles of iron, it is held that they were 

 carried into the tissues by inwandering leucocytes. 



It may be stated, then, as a reasonable probabil- 

 ity that micro-organisms are sometimes carried into 

 the deeper tissues by leucocytes which re-enter the 

 surface. 



Phagocytosis of bacteria by epithelial cells, par- 

 ticularly by the pulmonary epithelium, is known to 

 occur, but it is not known that the process is an 

 essential one for invasion. 



Some toxins are not readily absorbed by the nor- 

 mal mucous membranes, whereas others seem to be 

 taken up readily. In the absence of wounds, tet- 

 anus toxin, when ingested, causes no symptoms. 

 It is destroyed largely by the gastric and pan- 

 creatic juices, and this is the case also with diph- 

 theria toxin in test-tube experiments. The latter 

 has the power of causing necrosis of the mucosa, 

 and may be absorbed through the injured surface. 

 The toxin of hay fever is readily absorbed through 

 the conjunctiva and the mucous membrane of the 

 nose. Experimentally, ricin, a plant toxin, is 

 absorbed through the intestines, although the 

 amount required for fatal intoxication by this 

 route greatly exceeds that of the subcutaneous 

 injection. The toxin of the bacillus of botulism 

 is readily absorbed through the intestines of both 

 man and animals. 



Denudation When a micro-organism causes a primary des- 

 quamation of the mucous epithelium, it follows 

 that further penetration of the organism, as well 



