Studies in the Physiology of Parasitism

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Abstract
1.Certain bacteria which are normally termed saprophytic, viz. Bacillus subtilis and B. megatherium, are able to parasitize living potato tissue at a suitably high temperature or when the tissue is injected with water. 2.Within the group of four bacteria tested, there is a correlation between capacity to attack potato tissue and amount of pectinase enzyme excreted under standard conditions. 3.A qualitative difference between the pectinase enzymes of Botrytis cinerea and Bacterium carotovorum has been demonstrated. Preparations of the bacterial enzyme, which when tested on turgid potato discs of standard thickness were found to be weaker than Botrytis enzyme, were able to attack normal (subturgid) potato tissue, whereas the Botrytis enzyme failed to do so. No explanation of this difference is yet forthcoming. It does not seem to rest upon osmotic differences between the two enzymic preparations. 4.Rate of diffusion appears .to be a limiting factor in the attack of potato tissue by preparations of pectinase enzyme.