Disease of the Turnip (Hrassica napus). 445 



a single bacterium was selected and its development watched with the 

 capsule fixed under the microscope until the colony was sufficiently 

 large to transplant. Cultivations were also made by the method of 

 the hanging drop. A drop of gelatine bouillon from a test-tube con- 

 taining a very few bacteria was placed upon a sterile coverslip, and 

 then inverted over a sterile growing cell and examined under the 

 microscope. If the bacteria were too numerous, the preparation was 

 discarded and trials made until a hanging drop was secured with only 

 one or two bacteria. The growing cell was now fixed under the micro- 

 scope, so that a selected bacterium could be observed and the growth 

 of the colony noted. When sufficiently large the coverslip was 

 quickly inverted and the colony removed by the fine Unna's harpoon 

 to a petri capsule. In this way pure cultures were obtained, grown 

 from a single bacterium, which always gave rise to the characteristic 

 " White Eot," and left no doubt that this bacterium is the sole organ- 

 ism concerned in the disease. 



Pure cultures were also sown upon plants growing in the College 

 garden with exactly the same result. The decay commenced at the 

 point of infection and soon spread through the sound roots, eventually 

 producing the same white putrefying mass of rottenness. 



The bacterium can live for many generations as a saprophyte without 

 losing its virulence as a parasite. A stock obtained from a " white- 

 rotted " turnip growing in a field near Newcastle on September 10th, 

 1898, was isolated during that month, and after passing through 

 several cultivations in successive test tubes was finally put aside on 

 April 29th, 1899. On August 23rd two sound turnips were selected 

 in the College garden, and while still growing, the part of the roots 

 .above ground was washed with corrosive sublimate and afterwards 

 with sterile water ; a wound was then made with a sterile knife, and a 

 little of the culture from one of the test-tubes left undisturbed since 

 April 29th was introduced by a platinum wire. The turnips were then 

 covered over with a zinc cylinder, and, upon examination five days 

 after, on August 28th, the rot was found to have penetrated deeply 

 into the tissues, the larger half of the roots having become completely 

 rotten with all the distinctive characteristics of the true " White Rot." 

 In order to ascertain the precise action of the bacterium, and to 

 determine whether it produced any ferment capable of acting upon 

 the cell-wall in a manner similar to those of various parasitic fungi, 

 the method of precipitation by alcohol was adopted. A litre flask 

 was plugged, sterilised, and then filled about half-full with sterile 

 blocks of turnips, to which was added a small block upon which a pure 

 culture of bacterium had been sown ; a little sterile water was then 

 introduced, the flask closed as quickly as possible, and then well 

 shaken to distribute the bacteria. In twenty -four hours many of the 

 "blocks showed the characteristic action of the bacterium, and in the 



