Diffusion and intertraction

Abstract
The starting-point of this investigation was the phenomenon which Sir Almroth Wright described in the ‘Proceedings of the Royal Society,’ Series B, vol. 92. The original experiment is conducted by putting 5 or 8 per cent. NaCl in a test-tube or flat glass cell and allowing some blood serum to run slowly on the top of the NaCl. As soon as the fluids are brought into contact, a mass movement is started, the upper fluid being carried down into the lower and the lower into the upper. The characteristic appearances so produced are well described by the terms intertraction or pseudopodial interpenetration. By colouring the serum with a trace of some dyestuff (e. g., eosin) the inter traction phenomenon is easier to follow; or by having a layer of tannic acid or sulpho-salicylic acid in NaCl solution on the bottom, one sees after a short time (some minutes) a heavy precipitate in the lower interface. This system, serum on NaCl solution, presents a typical example of the intertraction phenomenon, as will be described in the following experiments, in so far that in the case of serum and NaCl solution both fluids are, so to speak, active and penetrate each other quickly, so that after some time (10 to 30 minutes) the contents of the vessel are a homogeneous mixture, as can readily be seen if eosin be used in the seruin. This result, the homogeneous mixing, is completed by ordinary diffusion, which very soon sets in after the intertraction has begun, from the numerous streams and droplets of the serum which come down in the NaCI solution.

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