Pethybuidgk and Mukphy — Bacterial Disease of the Potato. 17 



a few successive platings, the non-liqiiefiers were obtained in absolutely pnre 

 culture, it was found impossible to induce a rot in the tuber from them ; and 

 throughout our work we have never yet come across a non-liquefying organism 

 which causes such a rot. From what has been said, the great importance of 

 securing absolutely pure colonies by a succession of platings starting from the 

 original material is clearly demonstrated. 



With regard to the colonies of liquefiers, after successive cultivations, 

 these were inoculated into potato-tubers; and in all cases they produced the same 

 kind of characteristic rot. From each of the series a pure sub-culture of the 

 toxic organism was obtained, and from the comparative tests made of them 

 we have no reason to suppose that they differed amongst themselves ; on the 

 other hand, we have every reason for believing that they consisted of one and 

 the same organism only. 



Seeing that during the pre\dous year the method of inoculating by placing 

 the material on the surface of cut slices of fi'esh potatoes did not always give 

 satisfactorily concordant results, a slightly different method was adopted, 

 although the method mentioned was frequently used in addition. The 

 modified method employed was as follows : — Smalhsh or medium-sized tubers 

 were freshly dug for the purpose of the experiment, a shoi't portion of the 

 rhizome being left on each. They were thoroughly washed and scrubbed with 

 a soft brush in raiu-water ; and as the land in which the potatoes were grown 

 was reclaimed bog, it was an easy matter to get the tubers quite clean. They 

 were then dried in a clean towel, and the heel-ends of them were dipped into 

 a solution of mercuric chloride, which was allowed to dry on them. 

 Immediately before inoculation, the small projecting portion of the rhizome 

 was cut oif ilush with the surface of the tuber with a pair of scissors with 

 sterile blades ; and by means of a sterile, steel, lancet-pointed needle a stab 

 of about half an inch to an inch in depth was made into the heel end of the 

 tuber through the cut end of the rhizome. Into the stab thus made the 

 inoculating material, usually from a three days' old culture, was introduced 

 by means of a sterile platinum wire. After inoculation the tubers were placed 

 in covered glass dishes, and in every instance along with them control-tubers 

 were placed, which had received exactly the same treatment, except that the 

 inoculating material was not iutroduced into them. A convenient method of 

 sterilizing the steel needle and scissors was found to be that of keeping them 

 immersed in strong alcohol, and immediately before use lifting them out and 

 igniting the liquid adhering to them and letting it bm-n off. Thus sterility 

 was obtained and excessive heating of the needle and scissors avoided. As a 

 general rule, the inoculated tubers and their controls were kept at laborator}' 

 temperature. Some of the experiments, however, performed later on in the 



B.I. A. PROC, ^OL. XKIX., SECT. B. [C'J 



