The purpose of this note is to stress the importance of certain findings in recent studies on rickettsiae and to comment on the implications.
Biology. Two groups of workers studying the virulence and activity of rickettsiae have obtained results of fundamental importance in the biology of these micro-organisms. Bovarnick and Allen (1954) found that typhus rickettsiae of the Madrid E strain lost their toxicity for mice, their hemolytic activity, their respiratory activity, and their infectivity for chick embryos as a consequence of freezing and thawing in isotonic salt solutions; they showed that these properties could be partially restored by incubation of the rickettsiae in the presence of diphosphopyridine nucleotide, DPN, and Coenzyme A for as short a time as two hours at 34°C. Bovarnick and Allen further showed that the inactivation and subsequent reactivation is quite sensitive to the presence of low concentrations of sucrose during the process.