INTRODUCTORY NOTE. 



This volume which Dr. Langfeld has written is 

 intended as an introduction to the subject of bacteriol- 

 ogy, for the use of that large and increasing number of 

 people who are interested directly or indirectly in the 

 subject, but who have been unable to undergo any 

 practical training in it. I have had the opportunity of 

 reading the chapters before they went to press, and 

 have no hesitation in recommending the book to the 

 class of readers for which it is intended. The presen- 

 tation is simple and clear, and the author has carefully 

 avoided the use of terms and the discussion of questions 

 which would be unintelligible to beginners in the sub- 

 ject. It is his hope and mine that many may be led 

 through a study of these pages to undertake sufficient 

 practical work in the subject of bacteriology to permit 

 them to apply in their various occupations the principles 

 of this science so important in connection with medicine 

 and with the nursing of the sick. 



Lewellys F. Barker. 



Baltimore, Maryland. 

 March 20, 1907. 



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