ON IMMUNITY TO BACTERIA 351 



been discussed already, and we have seen reason to believe that 

 the chief regions in which it takes place are the lymphoid organs, 

 the lymph glands, bone-marrow, and spleen especially. These 

 organs appear to have as one of their functions the elaboration of 

 defensive antibodies as an internal secretion in response to toxins 

 and other bacterial products (free receptors, etc.) circulating in the 

 blood. We have also seen that the phagocytes, and especially the 

 polynuclear leucocytes, may act as sources of these bodies, but 

 that the evidence is less convincing than in the case of the 

 lymphoid organs. 1 



The local production of antibodies is probably more important, 

 since it takes place at the spot at which these substances are 

 required. As an example we may take Romer's demonstration of 

 antitoxin in the conjunctiva as a result of installations of abrin, 

 when no antitoxin had yet appeared in the general circulation. 

 The source of these antibodies, as first suggested by Whitfield, is 

 probably the lymphocytes, which form so important a factor in 

 chronic inflammatory lesions, and which occur after a few days in 

 the periphery of acute lesions. These cells do not act as phago- 

 cytes in vivo, though they may do so under experimental condi- 

 tions, and on any other hypothesis their presence in inflammatory 

 lesions is entirely inexplicable. We may feel certain, however, 

 that they are attracted there for some good purpose, and it is in 

 the highest degree probable that this purpose is the elaboration of 

 protective antibodies. It seems fairly certain that the source of 

 the haemic antibodies is the lymphocyte cells of the adenoid 

 tissues, and the cells of a chronic inflammatory lesion are exactly 

 similar. And in many cases if we examine the region in which 

 inflammation has taken place some time previously, we shall find 

 that the cells which were attracted thither have become organized 

 into definite adenoid tissue. 



It seems probable, too, that these small round cells are the basis 

 of the local acquired immunity, concerning which so little is 

 definitely known. After the bacteria have been destroyed the 

 polynuclear leucocytes remove the debris of dead tissues, etc., and 

 then retire, but the lymphocytes persist in the region for long 

 periods. During this time they are perhaps continuously elaborat- 

 ing small amounts of antibodies, and are certainly on the spot and 

 ready for action should a fresh infection occur. It is probable, 



1 More recent researches tend to point to the endothelial cells as the more 

 probable source of origin of the antibodies. 



