The recovery of bacteriophage from filtrates derived from heated spore-suspensions

In recent papers by den Dooren de Jong (1930, 1931) dealing with bacteriophages for B. megatherium the author states that of eighteen megatherium strains which he was studying three were lysogenic, that is, their broth culture filtrates contained bacterio-phages capable of causing lysis of other susceptible strains. Spores of the parent strains could survive exposure to a tempera-ture of 100°C. for five minutes, and the filtrates of the cultures derived from these heated spores showed all of the typical bacteri-ophage properties. The lytic principle itself was killed or inacti-vated by heating at 70°C. for five minutes. On the basis of these experiments he concluded that, as the bacteriophage alone was destroyed at 70°C., the principles found in the cultures arising from the heated spores must have been developed by the living cell itself and that, therefore, d'Herelle's theory of the living nature of the bacteriophage is not tenable. This conclusion seems warranted if we admit that all bacterio-phage present in a culture is actually destroyed by heating at 90 or 100°C. The principle, when free, undoubtedly is so destroyed or inactivated, but if some of it is incorporated in the spores when they are formed, it is not impossible that it may be protected by the same mechanism, whatever it is, that enables the spore to withstand temperatures lethal to vegetative cells. This would permit an alternative explanation. If the latter assumption is true, the lysogenic strains mentioned above may have been contaminated with bacteriophage whe