PREFACE XI 



Other chapters as possible. In the majority of cases each section 

 is complete in itself. 



These instructions are followed by information as to the inter- 

 pretation of the results which may be obtained, and this informa- 

 tion applies equally whether the medical man has made the 

 examination for himself or has obtained it ready-made from a 

 public laboratory. It, too, commonly happens that practitioners 

 feel themselves aggrieved because they get a negative report (as 

 to the presence or absence of Widal's reaction) on blood taken 

 during the first few days of an illness which turns out to be 

 typhoid fever, or are inclined to discredit bacteriological examina- 

 tions because diphtheria bacilli are found in throats which exhibit 

 no membrane and clear up in a few days without serious symptoms. 



In the second place, there are a few cases in which the investiga- 

 tion had better be made in a public laboratory. In these the 

 questions of what to send and how to send it are fully explained. 

 This is a most important point. A bacteriologist is not a magician 

 who is able to weave a spell if he has a small portion of his 

 victim's anatomy to work upon, and the materials must be taken 

 in the proper way if his results are not to be useless or even mis- 

 leading. This is well seen in the examination of the blood for 

 bacteria. In many cases the blood is drawn in such a manner 

 that it must necessarily be contaminated from the skin during the 

 operation, and is transmitted in vaccine tubes which were almost 

 certainly not sterile before being filled. Under such circumstances 

 the bacteriologist will probably report the presence of streptococci 

 or staphylococci, and the practitioner who does not understand the 

 fallacies of the examination may be led to make a diagnosis which 

 will be disastrous to his own reputation, and may be injurious to 

 the patient. 



Lastly, it need scarcely be said that this is not intended to be 

 a substitute for any one of the numerous excellent works on the 

 science of bacteriology which are current at the present time. 

 The practitioner is strongly recommended to supplement the very 

 meagre details concerning the life-history and pathogenic action 

 of the bacteria which are dealt with here by a study of one 

 of these text-books. Muir and Ritchie's admirable " Manual 

 of Bacteriology," Crookshank's " Bacteriology and Infective 



