Section IV., 1W06. [ 257 ] Trans. R. S. C. 



XIY. — Some of tlic Unsolved Frol/lcms of Immunity. 

 By Albeiît g. Xicholls. M.A., M.D., CM., 



Ai.sistant Prof s'sor of Patholnsy. McGill University: A.'jsistant Physician, 

 Montreal General Hospital; Pathologist to the Western Hospital, 



Montreal. 



Presented by Peof. AVesley Mills, M.D. 



(Read May 23rd, 1906.) 



Immunity is that property of living protoplasm which makes it 

 insusceptible to the action of agents that are ordinarily deleterious to 

 other organisms of a similar kind. From the point of view of the 

 therapeutist it may be defined as " cure in operation from the begin- 

 ning/' Immunity, which is the special peculiarity of the organism 

 from the earliest period of its existence, is termed naiural, innate, or 

 hereditary immunity. Immunity the result of causes influencing the 

 organism during its lifetime is called acquired immunity. Strictly 

 speaking, the word " inununity " denotes complete protection against 

 external noxœ, but it is not customary to confine its application within 

 such narrow limits. Complete or absolute immunity is rarely met wit'i, 

 but we have between this extreme and marked susceptibility all possible 

 grades of relative immunity. 



The phenomena of immunity are manifested in connection with 

 a great variety of substances. These are in most case- chem^enl i^i 

 nature and may be derived from the vegetable, mineral, and animal 

 kingdoms. 



A consideration of the subject of natural immimity gives rise to 

 many interesting and suggestive lines of thought. It has long been 

 recognized that certain organisms are more susceptible to the action 

 of deleterious agencies than are others. These differences are evidenced 

 with regard to species, races, families, individuals, and life-periods. As 

 a general thing, we find that the cold-blooded species of animals are 

 insusceptible in a considerable degree to the action of micro-organisms 

 that produce disease in warm-blooded animals, and vice-versa. ISTote- 

 worthy variations in Ihis particular are also found in the case of the 

 warm-ltlooded animals themselves. Human beings, for example, suffer 

 from typhoid fever and syphilis, diseases that, so far as we loiow, never 

 occur in the lower animals in the ordinary course of nature. Conversely, 

 many of the infective organisms that attack the lower animals never 



Sec. IV., 1906. 22 



