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.¢., 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. Metuop oF FIxaTIon By HeEat.. 
Slides or cover-glasses to’ be fixed by this method 
must be exposed to a temperature of 150° C. for 
