A spirochete found in the blood of a wild rat

Abstract

Of thirty nine wild rats (Mus decumanus) caught here at Morgantown one has shown a minute actively motile spiral organism in the blood. It is present in very small numbers and careful search with high magnification is necessary to detect its presence. In freshly drawn blood it appears as an elastic spiral rapidly darting about, as often with one end forward as the other, forth and back, rotating on its long axis as it goes. The movement is frequently too rapid for the eye to follow. The spiral turns appear quite permanent. At times a lashing movement of the whole body is seen but the organism straightens out quickly to its former shape. When caught among blood cells it jostles them about in a lively fashion, while it is itself invisible. This seems to be due to these flexuous movements of the whole organism. Actual contact of the spiral appears to be necessary before the blood cells are moved, which suggests that flagella are absent or too slender to make a visible impression on an erythrocyte.¹ The organisms are difficult to measure in the living condition but the greatest length observed is about 5 μ. Much shorter forms are recognizable in the fresh preparation, though harder to see on account of the more active movement. The refractive index of the parasite is not very great.

The parasite stains readily by the various modifications of the Romanowsky stain, and very intensely by the rapid method which I have recommended for clinical staining of Spirochæta pallida. 2 It takes a uniform deep violet red color. The measurement of a number of individuals shows a marked variation in length, the shortest forms, consisting of one and three quarters turns or nodes, having a length of 1.75 μ; the longest, consisting of three and one half turns, being 3.55 μ long.