THEORIES OF IMMUNITY. 



III. 



We come now to a discussion of Ehrlich's 

 theories in explanation of the same phenomena, 

 which are based upon the idea that the reactions 

 seen are primarily chemical in nature, although, 

 as will appear, it is impossible to neglect the 

 vital factor even in these theories. 



Dr. James Ritchie (Review of current theories 

 regarding immunity. The Journal of Hygiene, 

 1902, Yol. II., nos. 2, 3, 4) has published a 

 very elaborate and painstaking discussion of 

 these theories, the best and most complete that 

 has yet appeared in English. It is, however, 

 useful only for those who already have some 

 familiarity with the subject. 



It has been attempted, therefore, in what fol- 

 lows to condense the material gathered, to the 

 end that confusing details may not enter, and 

 that merely the main facts may be brought out. 

 The method adopted for illustrating the reac- 

 tions supposed to occur is entirely original, and 



40 



