PREFACE TO THE SECOND EDITION 



The call for a second edition of these Laboratory Direc- 

 tions has come in such a short time that many of the diffi- 

 culties encountered in the preparation of the first edition still 

 remain. The choice of subject-matter and the selection of 

 methods for a short elementary laboratory course become 

 more and more difficult with the rapidly increasing develop- 

 ments in bacteriology. The recognized etiological importance 

 of a number of bacteria which formerly were considered of 

 little significance necessitates, for the best results, an extension 

 of a knowledge of bacteriology beyond the differential charac- 

 ters and properties of a few pronounced pathogenic species. 



Experience with the first edition has clearly demonstrated 

 the advantage to both student and teacher of specific direc- 

 tions for a working basis in carrying out the various procedures 

 in a laboratory course. The exercises have been considerably 

 modified, four new ones added, and a few references appended 

 for the purpose of aiding students in familiarizing themselves 

 with the current literature on the subject. 



In revising these exercises new text and reference books 

 have been freely consulted. Valuable suggestions have also 

 been received from a number' of teachers and investigators. I 

 am especially indebted for such assistance to Dr. Theobald 

 Smith of Harvard University, Dr. Erwin F. Smith of the United 



