1. Prolonged and systematic examination of blood from swine with hog cholera has failed to reveal any formed element that could be identified with the etiological virus. Culture has likewise been unsuccessful.

2. The quantitative blood changes in hog cholera consist in a slowly progressive anemia, usually moderate in degree, and a rapidly progressive severe leucopenia affecting cells of the polymorphonuclear series most markedly but also including those of the lymphocytic series.

3. Incubation of hog cholera blood results in a further progress of the leucopenia, in vitro, if heparin has been used as the anticoagulant, but there is no significant change if potassium oxalate or sodium citrate has been used.

4. Consideration of the leucocytic reactions prevailing in experimental infection with B. suisepticus, in infectious enteritis, in swine influenza, following successful immunization against hog cholera, and following infection of cholera-sick swine with secondary invaders indicates that the leucocyte count would be of aid in the differential diagnosis of hog cholera.

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