168 BACTERIOLOGICAL DIAGNOSIS. 
Jenner’s stain is suitable for a study of the parasite of 
malaria, which it stains blue. It may be used for the 
detection of bacteria. 
3. Eosin and methylene blue used separately. 
In this method the films are to be stained with the 
eosin first and then with the methylene blue. Its 
successful application requires a certain amount of 
practice. 
The eosin used must be in watery solution, and the 
exact strength does not matter; four per cent. is a 
convenient strength to use. Most specimens of red ink 
(slightly diluted) will do quite well. The films are 
to be stained in this solution for three or four minutes; 
no harm will result if they are left in much longer. 
They are then washed and immersed in a saturated 
watery solution of methylene blue. ‘This is the diffi- 
cult part of the process, for no general rule can be 
given as to the length of time for which this stain must 
be applied ; it may be ten seconds, or it may be two or 
three minutes. The only safe way is to stain the film 
for a quarter of a minute, wash it, and then examine it 
under the low power of the microscope. If the film is 
properly stained the nuclei of the leucocytes will be seen 
as blue points which can be distinguish with great ease 
with the 2 inch objective. If they are not visible the 
methylene blue must be applied for about a quarter of 
a minute more and the examination repeated. When 
the nuclei are seen to be well stained the film is dried 
and mounted. 
This process gives results which resembles those 
afforded by Jenner’s stain except that the fine eosino- 
phile granulations in the polymorphonuclear cells are 
always less obvious and often quite invisible. It is 
also suitable for malarial parasites and bacteria. 
