INTRODUCTION [i] 



Importance of the study of immunity from a general point of view. Part played 

 by parasites in infective diseases. Intoxications by the products of micro- 

 organisms. Resistance of the organism to the invasion of micro-organisms. 



Natural immunity and acquired immunity. 



Immunity to micro-organisms and immunity to toxins. 



THE problem of immunity in relation to infective diseases is one 

 that not merely concerns general pathology but has a very important 

 bearing on all branches of practical medicine, such as hygiene, surgery 

 and the veterinary art. The prevention of disease by the production 

 of an acquired immunity is daily assuming greater importance. With 

 the object of arresting the multiplication and dissemination of 

 morbific germs, we are seeking, by artificial means, to render indi- 

 viduals, who may come in contact with them, refractory to their 

 pathogenic action. Patients who have just undergone a surgical 

 operation and women in child-bed are frequently in danger of 

 acquiring a post-operation disease or a puerperal affection ; we are, 

 therefore, striving to protect them by conferring upon them an 

 artificial immunity. 



The immunisation of animals useful to man is likewise a question 

 of such great importance to agriculture and to industry as to have 

 now become the object of legislation. 



This question of immunity is, however, apart from its practical 

 aspect, intimately connected with problems of pure theory. There 

 can be no question that the marked pessimism developed during 

 the century just closed was in a large measure prompted by 

 the dread of disease and premature death, scourges against which 

 humanity is as yet powerless. It is recognised that Byron and 

 Leopardi, the great poets of pessimism, both suffered from con- 

 genital anomaly and from incurable disease and that these maladies 

 cast a gloom over their poetry. Schopenhauer, the founder of the 

 B. 1 



