CULTIVATION OF THE HOG CHOLERA VIRUS.
The work of Hecke on the cultivation, of hog cholera virus was confirmed with ease. Virus was grown in the presence of fresh minced swine testicle in flasks containing Tyrode solution, on the chorioallantoic membrane of embryonated eggs, and on the surface of swine serum agar. In flasks it was grown for 14 transfers; while on eggs it was grown for 13 transfers, followed by an equal number of transfers on agar, making 26 transfers in all. Only one strain of virus was used and we do not know whether all strains can be cultivated so readily or whether we were particularly fortunate in the selection of the strain used. Neither do we know whether swine testicle is better than other tissues for growth. The cultured virus produces characteristic hog cholera when injected into swine, and its effect can be neutralized with commercial anti-hog cholera serum. No evidence of attenuation of the virus was obtained, the last culture being highly virulent when small amounts were injected. No evidence for the adaptation to the egg could be secured, since passages without swine testicle on the membrane or intravenously for 2 transfers resulted in a loss of the virus. No contaminating virus that might favor the cultivation could be detected by animal or egg inoculation. Not only has the virus been cultivated but it has been demonstrated in large amounts in the culture. Four suspensions containing slightly over 0.5 mg. of protein nitrogen produced typical hog cholera when 1 x 10(-6) cc. was injected, and one suspension made in the same way was active in one-tenth this amount. Few titrations on what is commonly known as hog cholera virus, i.e. the serum from acutely ill pigs, are available. We made one such titration and produced a delayed disease with 1 x 10(-5) cc. of infectious serum. It seems probable that the culture virus is more active than the commonly used virus and that its practical use in hog cholera vaccination and hyperimmunization would result in a considerable saving. All of the methods used yielded active cultures, but the serum agar method is the one of choice since larger amounts of suspension can be obtained with less labor.
Tenbroeck
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Department of Animal and Plant Pathology of The Rockefeller Institute for Medical Research, Princeton, New Jersey.