20 Predisposition and Immunity. 



influences. For example, cats are extremely sensitive to carbolic acid. 

 It is well known that some persons possess so marked a susceptibility tc 

 a number of substances and foods (as strawberries, mushrooms, crabs, 

 lobsters, cocoa or alcohol) that after partaking of them they experience 

 severe pain, vomiting and cutaneous eruptions, and in the same way are 

 apt to be severely affected by certain medicaments (chloroform or mor- 

 phine) ; they are influenced by such substances, as it were by poisons. 

 Such extreme susceptibility is known as idiosyncrasy (i'Sios, •peculiar; 

 i] ffvyKpd(ns, combination). 



As a rule, the predisposition or inimiiinty of individuals is 

 only a relative one ; that is, it is variable and of moderate degree, 

 may be increased or decreased, and is often only temporary. 

 Racial or specific immunity may also be but relative. Rabbits 

 are ordinarily immune to symptomatic anthrax, but now and 

 ?gain a rabbit is found to be susceptible to this disease upon 

 inoculation. Goats, horses and cattle are strongly resistant to 

 swine-erysipelas, but if large amounts of the virus are injected 

 intravenously they may show severe symptoms. Young dogs are 

 somewhat susceptible to anthrax ; older dogs less so. Young 

 sucking calves are very rarely afifected by "black leg" and usually 

 resist inoculation tolerably well ; but as soon as they begin to 

 eat vegetable food they become very susceptible to the disease 

 in question. Thus age and food are seen to have an influence 

 upon predisposition and immunity. How intimately connected 

 'the latter factor is may be inferred from the experiment, origi- 

 nally performed by Feser and afterward confirmed by others, in 

 which rats, if fed upon meat alone, are found as a rule to be 

 immune to anthrax, while if fed on bread they soon succumb to 

 inoculation with the virus. 



By experimentation it has been shown, moreover, that hunger 

 is a predisposing cause, that bodily overexertion (overheated ani- 

 mals), nutrition of restricted quality and excessive amount ( as a 

 diet too rich in fat) may have such depre'ssing influence that 

 animals subjected to them' readily succumb to injurious agencies 

 which they would otherwise bear, and particularly become less 

 resistant to infections. It is also true that certain, altered condi- 

 tions of the tissues afford especially vulnerable points for the 

 attack of pathogenic influences ; for example, gastric catarrhs, by 

 diminishing the production of hydrochloric acid, favor the 

 deposition and pathogenic action of bacteria which are otherwise 

 destroyed by the gastric juice. As a rule, previous disease leaves 

 as a sequel an increased disposition, the formerly affected tissues 



