. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 52 SPIROCHETES Indeed, when we think of the many ways in which syphilis spirochsetes may be transmitted from person to person it is sur- prising that the number of innocent cases is not much greater. The Spirochaetes. — The spirochsetes of syphilis, Spirochoeta pallida (Fig. 5C), vary in length from four to 14 ^ (^^Vtt to x^Vtt of an inch) and are immeasurably slender. They are more closely curled than the spirochsetes of relapsing fever, having usually from six to 14 very regular, short, sharp curls, q
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 52 SPIROCHETES Indeed, when we think of the many ways in which syphilis spirochsetes may be transmitted from person to person it is sur- prising that the number of innocent cases is not much greater. The Spirochaetes. — The spirochsetes of syphilis, Spirochoeta pallida (Fig. 5C), vary in length from four to 14 ^ (^^Vtt to x^Vtt of an inch) and are immeasurably slender. They are more closely curled than the spirochsetes of relapsing fever, having usually from six to 14 very regular, short, sharp curls, quite different from the long graceful curves of a relapsing fever parasite. The living organisms are very active and dart with great speed across a slide, threading their way between blood corpuscles or cells. The spiral turning of the body reminds one of the undulat- ing movements of a swimming snake. Another spirochsete, Sp. refringens (Fig. 5D), is often found associated with Sp. pallida. During the early stages of their sojourn in the body the spirochsetes can always be found in the primary and secondary lesions, and in the neighboring lymph glands. During the second phase of the disease and also toward the end of the first phase the spirochsetes occur in variable numbers in the blood, and very early make their way into the cerebrospinal fluid in the brain and spinal cord. After it was found that the spirochsetes actually invade the central nervous system, and cause diseases of it, it was supposed that this occurred only occasionally in late stages of the disease. During the last year or two it has been shown, however, that the great majority (80 per cent) of syphilitics show distinct pathological changes in the spinal fluid, due to spiro- chsetes in it, from the date of the primary sore, and are therefore possible candidates for syphilis of the nervous system. During the second phase the spirochsetes make a general invasion of the entire body, later showing some special
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