Page:Tropical Diseases.djvu/269

XII] indian-ink or Burri method is invaluable for showing up the spirochæte. The technique is as follows: One drop of suspected blood and one drop of indian ink (Pelican brand) are taken up in a platinum loop and mixed together on a slide. The spirochætes appear as white wavy lines on a dark background. Harrison suggests a modification of this method, substituting a mixture of collargol powder I part, distilled water 19 parts, for the indian ink. The mixture is well shaken up in a black bottle before use. The dark-ground method of illumination is admirably adapted for demonstrating these parasites in a living state. A very strong illuminant preferably a high-power electric light (Nernst lamp), not always procurable in the tropics—— is required.

The " infective granule " of Balfour.—— Balfour has called attention to an interesting phenomenon occurring in the spirochæte infection of fowls, the exact signification of which has not been determined, but which may have reference to the relapses that are so striking a feature in spirochæte infection. His observations have been confirmed by Fantham and others. In spirochæte-infected fowls certain minute highly refractile granules are to be seen in a proportion of the red blood-corpuscles. At one time Balfour considered that these granules resulted from the breaking down of the spirochætes which are frequently observed to enter, move about in, and coil up in the red cells. But by employing the dark-ground method of illumination he was led to conclude that these granules enter the corpuscles as granules, and that they are derived from spirochætes free in the liquor sanguinis. He describes the process of "granule shedding" as follows:——

" By the use of the dark-field method, and more especially by practising liver puncture on chicks at the crisis or on chicks which have been given a sufficiently large dose of salvarsan, I have found that in the liver in particular, also in the spleen and lung, the spirochætes undergo an astonishing change. They discharge from their periplastic sheaths spherical granules, and it is apparently these granules which enter the red cells, develop in them, and complete a cycle of schizogony. The appearance is very remarkable. If a well-infected chick be given a dose of salvaisan, the peripheral blood is soon