PEEFACE TO SECOND EDITION 



THE past few years have added greatly to our knowledge of the two 

 (lasses of pathogenic micro-organisms, bacteria and protozoa, repre- 

 M-nting respectively the lowest forms of the vegetable and animal king- 

 doms. The importance of the protozoa is now recognized, not only 

 because of the diseases known to be caused by them, but also because 

 of their possible connection with the exanthemata and syphilis. In 

 view of these developments it is obviously essential that the student 

 should be instructed in both fields. I believe that the inclusion of 

 both subjects in a single volume offers the advantages of convenience, 

 facility of instruction, and the presentation of comprehensive knowl- 

 edge. In the present edition the section on the Protozoa, excepting 

 malaria, was undertaken by Dr. A. W. Williams. The chapter on 

 Malaria is from the pen of Mr. L. B. Goklhorn, Instructor in Pathol- 

 ogy in the University and Bellevue Hospital Medical College. Needless 

 to say, the revision of the part on Bacteria has been thorough, so that 

 the book as a whole endeavors to reflect the latest knowledge in the 

 whole domain. This edition, like the previous one, has been written for 

 the student and physician rather than for the laboratory worker. 



In the preparation of this edition I greatly missed the active assistance 

 of Dr. Guerard, whose removal to a distant city prevented his co-opera- 

 tion, except in the reading of the proof. I am also indebted to Dr. 

 Cliarles Bolduan, Assistant Bacteriologist in the Research Laboratory, 

 for valuable help in preparing this work for press. 



I take this opportunity of acknowledging much valuable help from 

 the splendid work on the pathogenic micro-organisms edited by Kolle 

 and Wassermann. Several photographs from their Atlas have been used. 



W. H. P. 



XE\V YORK, 1905. 



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