SIGNIFICANCE OK ALLERGY 541 



h'aiiiK's that tuberculin allcriiy and iiniuunity are not necessarily 

 identical seems to be inherent in certain observations of Clawson 

 (1934) and others. The former reports that animals receiving 

 a heat-killed suspension of B.C.G. vaccine intravenously develop 

 definite immunity to the tubercle bacillus without becoming per- 

 ceptibly allergic to tuberculin as indicated by the Mantoux test. 



Birkhaug (1933), on the other hand, holds to the opinion that 

 allergy is an important and necessary factor in immunity to 

 tuberculosis. He studied the immunizing property of B.C.G. vac- 

 cine for guinea pigs over a period of two years and reports that 

 intradermal immunization yielded a more desirable and intense 

 allergy as well as a greater percentage of relative immune ani- 

 mals than intraperitoneal immunization. In his opinion B.C.G. 

 is incapable of producing progressive tuberculosis. 



Experimental and Clinical Studies of Allergy and Immunity in 

 Tuberculosis. — That these apparently' conflicting opinions are not 

 irreconcilable would seem to be apparent from a careful considera- 

 tion of the following experimental studies of Smith (1933), Lurie 

 (1936. 1939), Menkin (1938) and Cannon and Hartley (1938). 



While the research discussed in the preceding pages of this 

 chapter throws a great deal of light upon allergy and immunity in 

 tuberculosis, there is inherent in them certain artificial and ab- 

 normal conditions with which the student should be made ac- 

 quainted. The factors involved, Avhich may cause one to acquire 

 a misconception of what occurs in naturally acquired tuberculosis, 

 have been clearly set forth in a paper by Theobald Smith (1933). 

 He points out that in natural infection with the tubercle bacillus 

 the entry through the mucous membrane of the respiratory or ali- 

 mentary tract is not accompanied by mechanical injury to the 

 tissue, such as results from hypodermic injection, and the dosage is 

 limited to one or at most a few organisms as contrasted witli 

 relatively massive doses employed in experimental work. Fur- 

 thermore the organisms involved in natural infection have a rate 

 of multiplication and a metabolism that show the effect of a 

 parasitic environment, wherea.s in experimental work the organ- 

 isms have been acclimated to a saprophytic existence in artificial 

 media and possess an accelerated rate of growth. Their meta- 

 bolic products are perhaps essentially different from the organisms 

 that have been growing under parasitic conditions. Some of the 



