iv PREFACE. 



which organism Bordet and Gengou were incidentally, the first to 

 see. The articles have in general been arranged in chronological 

 order; an exception, however, was made in some of the latter 

 chapters (XXIV to XXX) which deal rather with the application 

 of more theoretical studies which precede. 



I am indebted to Professor Bordet, not only for consenting to the 

 collection of these articles, but also for furnishing the concluding 

 chapter and for certain suggestions and corrections. Doctor 

 Gengou was so kind as to abstract one of his articles for this publi- 

 cation. Thanks are also due to the publishers of the various jour- 

 nals in which these articles appeared for permission to translate or 

 to reprint them. 



F. P. G. 



BOSTON, August, 1909 



