20 
To Label Films 
Films should always be labelled as soon as possible, 
otherwise uncertainty and annoyance are sure to arise. 
The use of labels is not absolutely necessary. 
1. The most convenient method is that of writing 
on the slide with ordinary ink, which should be quite 
dry before placing in alcohol ; there is then no fear of 
the ink coming off. 
2. After making a dry film, as described above, 
the name, date, and other necessary information, are 
scratched on the film with the head or point of the 
needle. (Powell). 
To Fix Films 
Films must always be fixed, but this may be 
omitted where the stain also contains the fixative, e.g., 
in the Leishman and Jenner stains. 
1. Absolute alcohol .—This is the most convenient 
fixative. It is best kept in a glass-stoppered cylindrical 
jar about two inches in diameter. Methylated spirit 
can be used instead. Fix for three minutes or longer. 
2. Heat .—For the study of leucocyte granules 
this mode is indispensable. Place a crystal of urea 
(M. Pt. 131° C.) on the film to act as an indicator. 
Heat over a flame until the crystal just fuses. Allow 
to cool and remove the urea. The slide is then fixed. 
An alcoholic stain must still be used, e.g., Jenner, 
Ehrlich, etc. (or the haemoglobin will be dissolved 
out), but not Romanowsky, Giemsa or other watery 
stains. 
3. For other methods, and especially for the 
fixing of ‘ wet films/ vide ch. xxxiv. 
