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In 1938, when working on the chemical control of weeds in the then C.S.I.R. Division of Plant Industry, the author became confronted with the laboratory problem of assessing the relative toxicity of herbicides. An examination of the literature showed that two quantitative methods could possibly be used - the leaching of electrolytes from, tissue sections (Stiles and Stirk 1931), and tissue resistance changes as studied by Osterhout (1922) in marine algae. The former method depends on changes in the conductance of the external aqueous medium, and is inapplicable in the presence of electrolytes, e.g. buffering agents. A modification of the leaching method utilizes changes in the colour or optical density of the external medium when pigmented tissue is used. Comparatively little tissue is suitably pigmented, and it is unsatisfactory to use beetroot tissue as experimental material when one is faced with the problem of determining the injury caused by selective herbicides to the unpigmented roots of skeleton weed. Accordingly the author began to investigate the method utilizing changes in the electrical resistance of tissues, this method being applicable to all tissues even in the presence of electrolytes.
The investigations were interrupted by the last war, during which the author was seconded to the former Division of Metrology in the National Standards Laboratory, Sydney. On returning to the Division of Plant Industry at the end of the war he spent 6 months within the then Division of Electrotechnology, gaining experience in electrical measurements. After that he returned to the Canberra laboratories of the Division of Plant Industry, and extended his interests to other forms of injury (e.g. disease injury) and to other electrical studies included in this thesis.
The present thesis, which is intended as a contribution to biological science and not to physical science, is largely concerned with the fundamentals of the electro-diagnosis of injury. It therefore deals with theoretical principles before proceeding to biological studies of injury.
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