iv PREFACE. 



the practising physician, in that it enables him- to ob- 

 tain an intelligent grasp of the nature of the infectious 

 diseases. 



The methods used in the laboratory for the isolation 

 and identification of the typhoid, tubercle, and diph- 

 theria bacilli have been given with especial fulness, as 

 bacteriological examinations of the discharges of per- 

 sons suspected to have typhoid fever, tuberculosis, or 

 diphtheria are now generally made for these bacteria 

 in the laboratories of the health departments of even 

 the smaller cities, because of the manifest importance 

 to the public of knowing where such sources of infec- 

 tion exist. 



In preparing this book the best works have been 

 freely consulted. Of these, those of Fliigge and 

 Sternberg, on General Bacteriology, and those of 

 Abbott and Mallory and Wright, on Technique, should 

 perhaps be especially mentioned. 



My sincere thanks are due to Dr. Hermann M. 

 Biggs, the Director of the Bacteriological Laboratory, 

 and to my colleagues in it, who have so freely furnished 

 me with the results of their original investigations. I 

 wish also to especially acknowledge my indebtedness 

 to Dr. A. R. Guerard, who has given me invaluable 

 aid in the preparation of the book. The illustrations, 

 with the exception of those on malaria and cholera, 

 for which I am indebted to Drs. Welch and Dunham, 



