PREFACE TO THE FIEST EDITION. 



THE science of Bacteriology has, within recent years, become 

 so extensive, that in treating the subject in a book of this size 

 we are necessarily restricted to some special departments, unless 

 the description is to be of a superficial character. Accordingly, 

 as this work is intended primarily for students and practitioners 

 of medicine, only those bacteria which are associated with 

 disease in the human subject have been considered. We have 

 made it a chief endeavour to render the work of practical utility 

 for beginners, and, in the account of the more important 

 methods, have given elementary details which our experience in 

 the practical teaching of the subject has shown to be necessary. 



In the systematic description of the various bacteria, an 

 attempt has been made to bring into prominence the evidence of 

 their having an etiological relationship to the corresponding 

 diseases, to point out the general laws governing their action as 

 producers of disease, and to consider the effects in particular 

 instances of various modifying circumstances. Much research 

 on certain subjects is so recent that conclusions on many points 

 must necessarily be of a tentative character. We have, therefore, 

 in our statement of results aimed at drawing a distinction 

 between what is proved and what is only probable. 



In an Appendix we have treated of four diseases ; in two of 

 these the causal organism is not a bacterium, whilst in the other 

 two its nature is not yet determined. These diseases have been 



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