STUDIES ON THE ETIOLOGY OF HEARTWATER : I. OBSERVATION OF A RICKETTSIA, RICKETTSIA RUMINANTIUM (N. SP.), IN THE TISSUES OF INFECTED ANIMALS.

A Gram-negative, intracellular, coccus-like microorganism was found in cases of heartwater in the three species which are susceptible to the disease; namely, goats, sheep, and cattle. It was absent in the case of control animals, both normal ones and those dying of some. other diseases. The presence of this microorganism was definitely related to the febrile reaction. It was most easily detected in the renal glomeruli and in the small capillaries of the cerebral cortex but probably occurred throughout the body. The microorganism was a typical endothelial parasite, being restricted in distribution to the endothelial cells of the smaller blood vessels and to portions of such elements which had broken off into the blood stream. It was never observed to cause injury to the cells other than those incident to mechanical distention through accumulation within them of many individuals in large densely packed masses which were characteristically spherical. A typical attribute was the presence of several of these masses within the cytoplasm of a single endothelial cell. In view of the association of this microorganism with heartwater, a disease of ruminants, and thus far the only one in which microorganisms resembling Rickettsiœ have been reported, the designation Rickettsia ruminantium is proposed.