Vlll PREFACE TO SECOND EDITION 



that the blood-count has been thought to give the diagnosis 

 directly, without requiring any mental exertion on the part of the 

 physician or surgeon. It does so in some cases, but in most it is 

 to be regarded as an additional fact to be considered in making 

 a diagnosis — in many cases the chief and most important fact, but 

 one that must always be considered in conjunction with those 

 obtained by ordinary clinical methods. The results of a blood 

 examination are similar to those of any other physical examina- 

 tion ; they are easy to obtain, but often very difficult to interpret, 

 and, just as in the diagnosis of the diseases of the chest or the 

 nervous system, it requires much experience to make use of signs 

 which a student can elucidate. And, as in the case of the other 

 physical signs, the blood-findings are sometimes equivocal. It is 

 about as reasonable to discredit them on that account as to dis- 

 credit percussion of the chest because dulness does not always 

 indicate pneumonia. In spite of these difficulties the examination 

 of the blood is one that is more likely, in many cases, to give a 

 clue to what is actually taking place than is any other. As Cabot 

 puts it, " The blood is the only tissue which we can easily examine 

 during the life of the patient. Its relations to all other tissues are 

 such that it is typical of them all in a way that no other tissue is, 

 acting on all and being acted on by all." Here I have attempted 

 to give an elementary guide to some of the more important and 

 simple changes, and for further reference the practitioners are 

 recommended to consult one of the largest works on the subject, 

 such as those of Da Costa, Ewing, or Cabot, all of which are 

 admirable and full of valuable information. 



I have to thank Dr. Whitfield for the loan of the very admirable 

 photographs on Plates IV. and VI., and for revising the sections 

 on ringworm, etc., and Professor Schaudinn for the figures of 

 the spirochaete of syphilis shown on Plate V. 



W. D'ESTE EMERY. 

 March, 1906. 



