D. L. MACKINNON 
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human excrement. The rate of infection was pretty high—about 60 °/o- 
The parasites were always confined to the alimentary canal. The 
larvae of Scatophaga lutaria and of Homalomyia from the same feeding- 
grounds were even more richly infected than the adult insects. In the 
autumn I took a large number of these larvae into the laboratory, and 
kept them under observation at a temperature of 60 —i0 F., with a 
view to finding out what changes were undergone by the parasite during 
the insect’s development. Most of the larvae pupated, and a number 
of flies came out after about three weeks. 
I made attempts to cultivate the herpetomonads on agar-agar. The 
flagellates were taken from the gut of both kinds of larvae. They lived 
for two or three days on the new medium, but without multiplying, and 
in nearly every case assuming a rounded up or semi-encysted condition: 
the bacterial growth by that time had become so great that it was found 
impossible to isolate the flagellates in culture, and the attempt was 
abandoned. 
The gut of the fly or larva was examined for parasites in the usual 
way— i.e. it was dissected out in a drop of normal salt solution and 
examined under the microscope. If the parasites were present their 
characteristic movements betrayed them at once, even under a low 
power. The gut was then divided into three portions, and teased out. 
For Giemsa preparations I tried fixation with osmic acid vapour and 
with vapour of 40 °/ 0 formation, as well as the usual dry method. For 
adult flagellates I found the dry method exceedingly good, but for 
encysting and encysted stages the wet method gave much less de¬ 
formation. 
While admitting the great value and brilliance of the Romanowsky 
stains, I am of opinion that a more reliable cytological stain, such as 
iron-haematoxylin, should be used as a control wherever possible. 
Herpetomonads stained with iron-haematoxylin often present a very 
different appearance from those stained with Romanowsky stains (either 
after dry or wet fixation)—a circumstance that is at least suggestive in 
view of the interpretations placed on certain highly dubious structures 
described by authors from Romanowsky preparations. 
For iron-haematoxylin preparations, I spread the gut contents in a 
thin film on a cover-glass, and dropped it on the hot fixative (Schaudinn’s 
sublimate-alcohol) after the method recommended by Schaudinn. The 
stain did not always act very satisfactorily, but occasionally, when I got 
a good differentiation, the result was excellent and was an interesting 
commentary on the Giemsa preparations. 
