NATURAL IMMUNITY. 129 



X 



to those which we have learned to recognize as 

 infectious. The fact that an individual is free 

 from gout, diabetes or any other metabolic disturb- 

 ance, cannot be taken as indicating an immunity 

 from these diseases. Inasmuch as the metabolic 

 diseases appear to depend on the failure of certain 

 organs to perform their functions normally, for 

 some one or more reasons, we can only infer that 

 in those who are free from such diseases the corre- 

 sponding organs are in a state of normal activity. 

 Similarly an individual or race which is free from 

 an infectious disease because of lack of opportun- 

 ity to contract it would not be classed as immune. 



Immunity has no necessary relationship to the 

 degree of contagiousness of an infectious disease, 

 although some of the most striking and certainly 

 the most common examples of immunity are seen 

 in relation to such infections (as scarlet fever and 

 smallpox). Tetanus, on the other hand, which is 

 absolutely non-contagious, can likewise give rise 

 to a high degree of immunity. 



No medical fact is more widely known among Acquirecl 

 intelligent people than that an attack of certain immunity. 

 of our infectious diseases brings about some kind 

 of change in the patient's tissues which protects 

 him, or renders him immune, against further at- 

 tacks of the same disease. Inasmuch as he was 

 previously susceptible, the new property is an ac- 

 quired one, and he is now said to possess an ac- 

 quired immunity against this infection. 



It is also well known that many diseases which Natural 

 attack man can not be inoculated into animals, Immunit y- 

 and biologists are familiar with many examples 

 of immunity which are confined to particular spe- 

 cies. The lower animals apparently can not be in- 



