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Clara Raven
JAMA. 1941;117(23):2001. doi:10.1001/jama.1941.02820490075032.
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To the Editor:—  In referring to your editorial on Weil's disease (The Journal, Oct. 11, 1941, p. 1266), permit me to make one suggestion. In speaking of the laboratory tests in the diagnosis, the editorial states that "... dark field examination of centrifuged blood during the first stage and of the urine after the tenth day are the most important." Unfortunately, in practice the pitfalls involved in the direct examination of blood by dark field illumination are such that little reliance can be placed on this method alone, even by experienced laboratory workers.Recently I had occasion to speak with Dr. E. A. Fennel of Honolulu on this very subject. I had just completed a study on canine leptospirosis (Canine Leptospirosis in Pennsylvania, J. Infect. Dis.69:131-137 [Sept.-Oct.] 1941). In this study numerous blood specimens were examined serologically (agglutination-lysis test) and also by direct dark field illumination of centrifuged blood


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