56 
PB0PIIYLAX1S OP MALARIA. 
The dissection of mosquitoes .—To many the thought of dissecting 
a mosquito conjures up an amazing amount of difficulty, largely 
owing to the small size of the object to be dissected. As a matter 
of fact anyone possessing the most rudimentary knowledge of labo¬ 
ratory technique should have no trouble in dissecting these insects 
and demonstrating the presence or absence of malarial infection in 
them after having once been shown the really simple technique. 
In order to make good dissections the following apparatus is 
necessary: Microscopic slides and cover glasses, fine dissecting 
needles, a good dissecting microscope, and some normal salt solution. 
A compound microscope, of course, is necessary for studying the 
development of the malaria plasmodia, but malarial infection of 
the mosquito may be demonstrated, in many instances, with the high 
powers of the dissecting microscope. The parts of the mosquito of 
special interest to one engaged in the prophylaxis of malaria are the 
salivary glands and the portion of the mid-gut of the mosquito 
known as the stomach. 
Dissection of the salivary glands. —To make a perfect dissection 
of the salivary glands of the mosquito requires considerable skill, 
but it is comparatively easy to secure portions of the glands suffi¬ 
ciently perfect to allow of demonstrating the sporozoites. 
The salivary glands are situated within the thorax, lying ventrally, 
commencing at the posterior portion of the neck and ending at the 
level of the first pair of legs. The simplest way of securing them 
for examination is to cover the insect with salt solution and place 
it upon the stage of the dissecting microscope in such a position that 
the head is toward the dissector's hand. Then, with the needle in 
the left hand steadying the thorax, the chitinous covering of the 
thorax just back of the neck is incised, and then gentle traction is 
made with the needle in the right hand upon the head, separating it 
gently from the body. If the operation has been successful it will 
be noted that a minute bit of white tissue has been extracted with 
the head, and upon examination with the compound microscope it 
will be observed that in this bit of tissue lie the salivary glands, or 
portions of them. This tissue should now be removed from the head 
with a fine needle and placed upon a microscopic slide in a drop of 
normal saline. 
In order to determine the presence of malaria sporozoites the 
preparation should be covered with a cover glass, gentle pressure 
applied, and examined with a one-sixth inch or one-twelfth inch 
objective. If sporozoites are present they will appear as fine, hyalin, 
curved rods, lying within the cells or ducts of the gland or free in 
the salt solution in great numbers. They often occur in masses or 
side by side and measure about 14 micros in length. 
