Animal spirochætes of economic importance include:—
S. anserina, highly pathogenic to geese.
S. gallinarum (= S. marchouxi) in fowls. (See p. [119].)
S. theileri in cattle and S. ovina in sheep also occur in Africa; their pathogenicity is not clear.
S. laverani (= S. muris), occurring in the blood of and pathogenic to mice, is probably the smallest spirochæte from the blood, being only 3 µ to 6 µ long.
Numerous spirochætes have been recorded from the guts of various mammals, birds, fishes, amphibia and insects.
Cultivation of Spirochætes.—Cultures of spirochætes have been made with little success or with great difficulty until comparatively recently, when Noguchi (1912) devised a means whereby he has cultivated most of the pathogenic spirochætes as well as some Treponemata.
Noguchi has now cultivated S. duttoni, S. recurrentis, S. rossii, S. novyi and S. gallinarum from the blood; S. phagedenis[157] from human phagedænic lesions; S. refringens[158] and spirochætes from the teeth.
His method is as follows:—
A piece of fresh, sterile tissue, usually rabbit kidney, is placed in a sterile test-tube. A few drops of citrated blood from the heart of an infected animal, e.g., rat or mouse, is added, and about 15 c.c. of sterile ascitic or hydrocœle fluid is poured quickly into the tube. Some of the tubes are covered with a layer of sterile paraffin oil, others are left uncovered. The tubes are incubated at 37° C. The best results are obtained if the blood is taken from an animal forty-eight to seventy-two hours after it has been inoculated, that is, before the spirochætes reach their maximum multiplicative period in the blood. The presence of some oxygen seems indispensable for these blood spirochætes, and they fail to develop in vacuo or in an atmosphere of hydrogen.