W. A. Millard 159 



On the other hand, it may be recalled that in 1890, Bolley (13) isolated 

 a bacterium which he claimed was able to reproduce Scab and pointed 

 out that in choosing his material for isolation of the organism, he avoided 

 such scabs as were "blackened or pitted." 



Again, in 1915, Pethyb ridge (W) writing on the "Supposed causes of 

 Brown Scab," refers to Thaxter's organism and says: "Although some 

 writers have gone so far as definitely to ascribe some of our scab to this 

 organism, no scientific evidence appears yet to have been published 

 proving that the said organism is really responsible for our ordinary 

 potato scab." 



In 1907, a contribution to our knowledge of the subjeict was made 

 by Seton and Stewart (15). These investigators showed that Common 

 Scab could not be produced in sterilised soil and this work was followed 

 in 1915 by Pethybridge and Fannin (lo) who proved conclusively that the 

 theory of mechanically produced Scab was untenable. 



This work received confirmation from some unpublished experiments 

 carried out in 1914 by the present writer, and in 1915 by Mr T. Laycock, 

 then Assistant Lecturer in Agricultural Botany at this University. 



In view therefore of the general uncertainty on the subject in this 

 country, it was thought highly desirable to make an a priori investigation 

 of the cause of Common Scab and this was carried out concurrently with 

 some work on remedial measures, a popular report (17) of which has already 

 been published. 



Isolation of the Organism of Common Scab. 



This was begun in 1916, and in the subsequent absence of the writer 

 on war service, the primary work of isolation together with the study of 

 the morphological and cultural characteristics of the original cultures 

 obtained was carried out by Miss K. Sampson, then Assistant Lecturer 

 in Agricultural Botany at this University. The writer takes this oppor- 

 tunity of expressing his admiration of Miss Sampson's excellent work 

 in this respect and his gratitude to her for placing her notes and cultures 

 at his disposal on his return. 



In the selection of material no choice was made of any particular 

 type of scab, but scabbed potatoes were taken from various samples 

 which came in in the ordinary course of advisory work. No attempt was 

 therefore made in this early work to establish any relation between the 

 type of scab and the culture strains isolated. 



The material for inoculation was taken in the majority of cases from 

 young unruptured scabs, but a few mature and ruptured scabs were also 



11—2 



