CHAPTER VI 

 NATURAL AND ACQUIRED IMMUNITY 



Natural Immunity. — Species Differences in Immunity. — The 

 two infectious agents that caiLse cattle plague and chicken cholera 

 respectively are unable, under natural conditions, to produce dis- 

 ease in man. Conversely, the infectious agents that cause syphilis, 

 gonorrhea, Asiatic cholera, measles and a few other diseases pe- 

 culiar to man, never, under natural conditions, produce these dis- 

 eases in the lower animals. Dogs, cats and rats are relatively re- 

 sistant to ])neumococcus infection whereas man and guinea pigs 

 are quite susceptible. Rats can ingest relatively large doses of 

 botulinus toxin with apparent impunity whereas man and guinea 

 pigs succumb following the eating of exceedingly small amounts. 

 Coriell and Sherwood* found that cats possess almost solid im- 

 munity to .strains of salmonella oi-ganisms highly virulent for mice 

 as well as to .strains of B. anthracis, P. tuJarensis and a strain of 

 vaccine virus that is exceedingly virulent for rabbits. On the 

 other hand they found cats moderately susceptible to trichina in- 

 fections, and Leasure (1934) observed cases of fatal feline virus 

 enteritis. 



Racial Differences in Immunity. — Occasionally susceptibility 

 and resistance are found to correlate with racial differences. 

 Algerian sheep are said to show a much higher resistance to anthrax 

 than our domestic sheep and various races of mice differ in their 

 resistance to a number of infectious agents. Bay-Schmith (1929) 

 reports that diphtheria does not occur among the Eskimos although 

 the Schick test indicates that the normal percentage of susceptibles 

 exists among them. Sherwood, Nigg and Baumgartner (1926) ob- 

 served a similar phenomenon as regards scarlet fever among full- 

 blooded American Indians. They rarely have the disease although 

 the Dick test indicates a high percentage of susceptibles in the age 

 group of five to fifteen years. Toyoda, Moriwaki and Futagi 

 (1930) have compared the percentage of positive reactors to scarlet 

 fever toxin among comparable groups of adult Chinese and 

 Japanese. The ratio of susceptibles within the two races is as 1 

 to 2, while the morbidity statistics show equal susceptibility to 



*Unpublished work. 



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