CHAPTER X 



ACQUIRED IMMUNITY 



Theories of immunity The kind of diseases against which immunity 

 may be acquired Pasteur's theory Chauveau's theory The theory 

 of chemical neutralization The theory of habituation Rabies 

 Small-pox Anthrax Snake- venom The rationale of acquired 

 immunity Syphilis. 



186. THE literature of immunity is so large, and still 

 increases with such bewildering swiftness, that it is not easy 

 for any one outside the ranks of professional bacteriologists to 

 keep in touch with it. Owing, doubtless, to the novelty, 

 magnitude, and difficulty of the subject, the multitude of the 

 workers, and the keenness of their competition for success 

 and fame, observations and deductions, which later research 

 proves erroneous, are published with unusual frequency in 

 this branch of science. The task of the learner, however 

 willing, is thereby rendered doubly difficult. I approach this 

 part of my subject, therefore, with the greatest diffidence. 

 An amazing number of theories concerning the nature of 

 acquired immunity have been propounded, most of which 

 have already crumbled under the assaults of facts sub- 

 sequently discovered. One or two recent morphological or 

 chemical hypotheses depend on surmises which cannot be 

 tested by an appeal to ascertained facts, and, therefore, like 

 theories of ancestral units, are incapable of direct proof or 

 disproof. 



187. Presumably acquired immunity against a disease, since 

 it is a beneficial development arising as a regular consequence 

 of experience, is comparable to, is of the same nature as, 

 other acquirements which arise in the individual as a 

 regular result of use. In other words, presumably it arises 

 because and when the organism " gets used " to that particular 

 disease. Presumably also the inborn power of acquiring 



This chapter has been adapted from articles which appeared in The 

 Lancet (Sept. 11, 1897) and The Monthly Review (Jan. 1902). 



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