INFECTION AND IMMUNITY. 421 



torious, and are said to be resistant or to possess immun- 

 ity to this particular form of infection. 



It is a common observation that certain human beings 

 and animals are more susceptible to the different forms 

 of infection than are others, and that some are appar- 

 ently not at all liable to particular diseases; in other 

 words, they are naturally immune to the maladies. 



Again, it is often observed that an individual or ani- 

 mal after having recovered from certain forms of infection 

 has thereby acquired protection against subsequent at- 

 tacks of like character ; in other words, they are said to 

 have acquired immunity to this trouble. 



The problem involving the explanation of these inter- 

 esting observations has afforded material for reflection 

 and hypothesis for a long time, but it is only through 

 investigations that have been conducted during the past 

 few years that it has met with anything approaching 

 reasonable solution. 



Conspicuous among the observers who have endeav- 

 ored to explain the modus operandi of immunity may be 

 mentioned Chauveau, Pasteur, Metchnikoff, Buchner, 

 Fliigge and ^his pupils (Smirnow, Sirotinin, Bitter, Nut- 

 tall), Fodor, and Haukin, and in the following pages we 

 will present briefly the result of investigations by these 

 various authors. 



In 1880 Chauveau 1 suggested an explanation for the 

 phenomenon of immunity that has since been known as 

 the retention hypothesis. It is, in short, as follows : That 

 the immunity commonly seen to exist in animals that 

 have passed through an attack of infection, against a 

 subsequent outbreak of the same malady, and likewise 



1 Comptes-rendus, etc., July, 1880, No. 91. 

 19 



