552 BACTERIOLOGY. 



or species, that has originated during his life from the 

 stimulation of his integral cells by one or another of the 

 specific infective irritants that may have been purposely 

 introduced, or accidentally gained access to his body. 



Active Immunity. Acquired immunity may be either 

 active or passive in character. Active immunity is 

 that form which is seen after recovery from infection 

 acquired in a natural way, or from infection induced by 

 the injection of dead or living organisms or the poisons 

 peculiar to them. 



Passive Immunity. Passive immunity is that form 

 in which protective substances that have been generated 

 in a susceptible animal by one or the other methods of 

 immunization are transferred directly from that animal 

 to a normal animal by the injection of the blood serum 

 of the former into the tissues of the latter. The latter 

 being as a rule at once protected. The antitoxic serums 

 have been employed most frequently to bring about 

 passive immunity. The protective value of diphtheria 

 antitoxin in those that have been exposed to infection is 

 well established. The use of tetanus antitoxin for pro- 

 phylactic purposes is also recommended in cases where 

 there is a possibility of the development of tetanus. 



VACCINATION AGAINST BACTERIAL DISEASES. 

 The employment of various prophylactic measures 

 against infectious diseases has received much attention 

 in recent years. The measures employed in different 

 diseases vary somewhat, though in general the principles 

 are similar. 



The first measures of this nature that were employed 

 on a large scale are those of the Haffkine vaccination 

 against cholera and plague by means of cultures that 



