Page:Tropical Diseases.djvu/69

II] The parasite as a means of diagnosis.—All of these multiform appearances the student must learn to recognize and interpret. Skill in this is merely a matter of time, practice, and reflection. Given these, the student should be able not only to diagnose by the microscope malarial infection, but also to recognize the type of any particular infection, the period of the fever cycle, and, it may be, the severity of the case. For diagnosis in malaria, therefore, skill in the microscopical examination of the blood is of the utmost value, and no pains should be spared by the practitioner in malarious countries to acquire it. In acute untreated malaria the parasite may be detected practically in every case. Thus in 616 cases Thayer and Hewetson—except in two or three instances where the patient's blood was examined only during convalescence—found it in every instance. The best authorities are equally emphatic on this point. Personally, I can assert that since I became familiar with the subject I have never failed to find the parasite in any acute untreated malarial case I have had a proper opportunity of examining. Whenever in a case of acute disease, supposed to be malarial, I have failed to do so, the case has turned out to be of quite another nature.

Bearing of quinine on microscopical diagnosis.—It is of little use to examine the blood for the intra-corporeal forms of the malaria parasite after full doses of quinine have been taken; the drug rapidly brings about the disappearance of this phase of the parasite. The crescent alone is unaffected by drugs, and in suitable cases may be found for days after the patient is cinchonized.

On staining malarial blood.—As a general rule, the beginner should work only with unstained preparations of fresh liquid blood. To the unpractised, staining is full of pitfalls. In such circumstances it must not be relied on for purposes of responsible diagnosis. To the experienced microscopist and diagnostician, and for the study of the morphology of the parasite, staining is of the highest value; moreover, some such method must be employed should