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30 LOCAL IMMUNITY 



attacks the bones, and rarely any other tissues. Some of the best 

 examples may be taken from diseases that spread by continuity 

 from one tissue to another. Thus the gonococcus in either sex 

 spreads along the urethra with ease, but seldom involves the 

 mucous membrane of the bladder ; it practically never attacks the 

 vaginal mucosa (in adults), but spreads from the cervical to the 

 corporeal endometrium, and thence to the Fallopian tubes, but 

 comparatively rarely goes farther and produces a general peri- 

 tonitis. Diphtheria, too, though it may spread in any direction, 

 seldom creeps down the oesophagus. Many other examples might 

 be quoted. 



There are marked differences in regard to local immunity 

 between the child and the adult. The most marked example, 

 perhaps, is in the almost perfect local immunity of the scalp to 

 ringworm in adults, which contrasts so markedly with the absolute 

 susceptibility of children, whereas the susceptibility of the skin of 

 the body to the same parasite is, if anything, greater in the former. 

 In most cases of differing immunity at different ages the child is 

 more susceptible, just as its resistance to general diseases is less, 

 and the few exceptions that may be quoted are perhaps rather 

 apparent than real. 



Local immunity may be natural or acquired. Passive im- 

 munity, of course, cannot be local for long, as any serum which 

 is injected will rapidly diffuse away and be removed by the 

 lymphatics and blood-stream. The cases mentioned above are 

 all examples of natural local immunity. The difference between 

 the reactions of the tissues of children and adults do not neces- 

 sarily point to the acquisition of any active immunity in the sense 

 in which the word has been denned above, but rather to the 

 general rise in resisting power accompanying the general improve- 

 ment in strength and vitality, and in some cases, perhaps, to an 

 actual maturation of the tissues, as in the case of the adult vaginal 

 mucous membrane, which is immune to the gonococcus, whereas 

 the thin and immature infantile membrane is susceptible. The 

 immunity of the adult scalp to ringworm also is not acquired, 

 using the word in the narrow sense, for it occurs apart altogether 

 from an attack of the disease. 



Our knowledge of acquired local immunity is very incomplete ; 

 it is a difficult subject for research, and more attention has been 

 paid to general immunity. A little consideration will demonstrate 

 the fact of its occurrence. For example, when a person develops 



