164 BACTERIOLOGICAL DIAGNOSIS. 



The author is of opinion that it is best to adopt the 

 cover-glass method, as he has found that it presents 

 fewer difficulties for beginners ; this is not the universal 

 experience, and it is a good plan to try both and adopt 

 that with which you get the best results. 



FIXATION OF BLOOD FILMS. 



If films are required simply for bacteriological pur- 

 poses (i.e., to search them for bacteria) they may be 

 fixed by passing them three times through the flame, 

 just as if they were ordinary films. This, however, is 

 not to be recommended in the study of the cells of the 

 blood or of the parasite of malaria, though it answers 

 very well in skilful hands. Three methods should be 

 learnt, the method by heat, the alcohol and ether 

 method, and the formalin method. Of these the first is 

 necessary if Ehrlich's triacid stain is to be used, but the 

 others are perhaps better for other stains. In addition 

 to these we must mention that if Jenner's stain is used 

 a preliminary fixation is unnecessary, as the fluid fixes 

 the film and stains it at the same time. This is the 

 method of blood examination which is most suitable 

 for practitioners ; and it is doubtful whether it is not 

 also the best for the most accurate and delicate 

 scientific research. 



I. METHOD OF FIXATION BY HEAT. 



Slides or cover-glasses to be fixed by this method 

 must be exposed to a temperature of 150 C. for 



