Microscopical examination.—The beginner will save time if he gets someone who is familiar with the necessary technique, and with the appearance of the parasite in the blood, to give him one or two lessons. Accuracy and quickness can be acquired only by practice. It is a good plan to practise preparing films from one's own blood.
The examination is best conducted with a 112 in. oil immersion lens, a rather low eyepiece, a substage condenser, and a good but not too dazzling illumination. It is practically useless to work with any objective lower than 112 in., or without a substage condenser.
It is not always possible to choose, but, if practicable, a case of quartan infection should be selected for examination in the first instance. Failing a quartan, a well-defined benign tertian infection might be chosen. Failing either of these, a long-standing case of recurring malaria with marked cachexia will afford the next best opportunity. It is best to examine the patient's blood just before or at the time of rigor. In quartans and benign tertians, at the time named, there should be little difficulty in discovering large parasites; in the case of these infections, attention is called to the relatively large parasites by the abundance of coarse pigment they contain. In the blood of malarial cachectics with recurring febrile attacks it is generally an easy matter to find crescents and crescent-derived spheres, as this form of the parasite is of considerable size, carries abundance of pigment, arid possesses a very definite and striking shape.
When the beginner has learnt to recognize the larger forms of the parasite, he will have begun to appreciate what sort of body he has to look for; thereafter he should be able to educate himself, and to pick out the smaller and intermediate forms.
In proceeding to make his first examination of a liquid blood slide, the beginner, in the first instance, should confine his attention to the "single-layer zone." Field after field of this he must pass in review, carefully scrutinizing the interior of every
