The kidney of guinea pigs infected with the H37Rv and BCG strains of M. tuberculosis showed a diminution in succinic dehydrogenase activity when measured by the tetrazolium technique. This effect was also seen in the liver and spleen of animals infected with the BCG strain. Sensitized animals showed similar results when given tuberculin in sublethal doses. The succinic oxidase was also low in the kidneys of animals infected with the H37Rv strain. The depressed enzyme activity of the tissues of infected animals could be restored to normal by addition of normal tissue extract or dialysate. This suggests that the alteration in tissue metabolism observed in tuberculosis may depend upon the loss of some as yet unidentified factor important for succinic dehydrogenase activity.

In rabbits subjected to profound damage of the blood-forming tissues by the use of benzene and mechlorethamine hydrochloride, no impairment of efficiency in the splanchnic removal of M. aureus from the blood stream could be demonstrated by a method involving catheterization of the hepatic vein. All evidence continues to indicate that a bacteriemia cannot be maintained unless the organisms are introduced constantly into the blood stream from some source. The importance of the leukocyte in the establishment and clearing of the bacteriemias appears to lie in its phagocytic activities at the local source of the bacteriemia rather than in any quantitatively significant phagocytosis of organisms circulating in the blood stream. The present studies suggest that in the study of the leukopenic state attention should be directed more especially toward the identification and eradication of the local source of organisms.

1. By a method of hepatic venous catheterization previously described, comparative data have been obtained concerning the removal of pneumococci from the splanchnic circulating blood of the intact rabbit in bacteriemias secondary to a dermal infection and in bacteriemias induced by a continuous infusion of organisms into the blood stream. The average splanchnic removal in secondary pneumococcal bacteriemias was 8 ± 14 per cent (S.D.), in induced bacteriemias 9 ± 15 per cent (S.D.). 2. Similar data were obtained in induced M. aureus bacteriemias in normal rabbits and in induced M. aureus bacteriemias superimposed upon pneumococcal bacteriemias secondary to dermal infection. The average splanchnic removal of M. aureus in normal rabbits was 62 ± 20 per cent (S.D.). The splanchnic removal of M. aureus in rabbits with a simultaneous pneumococcal bacteriemia of infection was of the same order of magnitude as in normal rabbits. 3. The efficiency of the mechanism of splanchnic removal for a given organism is an important factor in the establishment and maintenance of a bacteriemia. Present evidence indicates that the maintenance of a bacteriemia requires a constant introduction into the blood stream of organisms from some source. 4. Pneumococci do not acquire a resistance to removal from the splanchnic circulating blood during the course of fatal infection in rabbits. 5. No final exhaustion of the mechanism of splanchnic removal can be demonstrated in fatal pneumococcal bacteriemias in rabbits.

A description is given of a slide cell whereby the rate of migration of very small amounts of leucocytes can be followed and measured. The migration of polymorphonuclear leucocytes was found to be inhibited by virulent tubercle bacilli pathogenic for the class of animal (mammal or bird) from which the leucocytes were obtained; it was not affected by the avirulent variants of these microorganisms, or by bacilli pathogenic for animals of the other class. Tests failed to disclose that the inhibition of leucocytic migration resulted from any gross damage caused by the bacilli to the leucocytes.