[Deep freezing of Babesia ovis in liquid nitrogen]

Comparative investigations were carried out to determine the optimal concentration of glycerin and dimethylsulfoxide in deep freezing of sheep erythrocytes infected with Babesia ovis. The blood was obtained from experimentally infected weaned lambs in the phase of acute parasitemia. Equal blood samples, mixed with the same volume of 2-, 3-, 4-, and 5-molar concentrations of the two cryoprotective agents as well as blood samples without such agents were frozen by the slow and the fast method up to--75 degrees C and kept in liquid nitrogen. The cryoprotective effect was evaluated by the hematocrit level of the samples of various concentrations in comparison with samples having no cryoprotective agent, frozen under one and the same conditions and by biologic experiments with susceptible weaned lambs. It was found that 4-molar concentrations of glycerin and dimethylsulfoxide produce an optimal cryoprotective effect, which, with the slow method of freezing was 64 per cent for glycerin and 60.7 per cent for dimethylsulfoxide. Blood frozen under such conditions and stored up to 6 months in liquid nitrogen retained its virulence.