35 



Among the bacteria isolated, Koning claims to have found the 

 species concerned ia this remarkable neutral fermentation, and which 

 imparts the aroma and flavour desired, and thus confirms Suchsland's 

 results. He states that tobacco infected with the specific bacteria, 

 fermented and made up, and then handed to experts, was seleoted by 

 the latter as the superior from specimens containing other kinds. There 

 is more than a touch of the dramatic in this scene of the experts 

 sitting down to smoke a pair of cigars each, in packets of two, and 

 labelled a and b, c and d, &c, only ; but the evidence appears con- 

 clusive. 



During the last ten years increased attention has been drawn to a 

 disease of tobacco leaves, which causes irregularly alternating light 

 and dark patches, and is known as the " Mosaic disease." Koning has 

 established that this is infectious, and is carried through the fields by 

 the fingers of the workmen who " top" the growing plants by pinch- 

 ing off the buds. He has examined the various fungi known to cause 

 leaf -diseases in tobacco, and cannot refer it to these, and the presump- 

 tion that it is a bacterial disease was strengthened by finding that 

 certain manured soils were almost sure to have badly disease 1 plants 

 on them ; and that experiments showed that if a bit of diseased leaf, 

 or a little of the sap from such is rubbed into a wound, the young 

 leaves formed above the wound contract the disease. The s lme result 

 follows if such sap is placed at the roots of healthy plants. But in- 

 fection fails in all these cases if the sap is previously boiled. 



Here may be mentioned that Adolf Mayer had proved the infectious 

 nature of the filtered sap in 1885, and Beijerinck, working at this 

 disease a short time ago (1898), had come to the conclusion that since 

 no organisms could be isolated from the sap — the infectious nature of 

 which he also proved — which will reproduce the disease, and since the 

 sap filtered through porcelain still infects the plants, unless it was 

 previously sterilised by heating, the causal agent must be a contagium 

 vivum fluidum — a something of the nature of a poisonous enzyme, which 

 not only diffuses through the plant-membranes — e.g., the cell- walls of 

 root-hairs — but increases as it passes from cell to cell. 



Koning confirms Beijerinck's principal results, but concludes that 

 since the infecting fluid may be heated to 1Q0°C. for a few minutes 

 without losing its powers, whereas alcohol and glycerine destroy the 

 virulence, as also does repeated filtration through porcelain, the active 

 agent is an extremely minute organism, which can traverse the pores of 

 a filter. He compares the results with those obtained with the virus 

 of various animal diseases from which no organism has as yet been 

 isolated. 



It should be borne in mind that the existence of organisms small 

 enough to pass through a porcelain filter has been accepted by several 

 authorities. 



It thus appears that — without regarding the work as quit? conclusive, 

 which it is not, — we have here important contributions to s)veral most 

 weighty biological questions centered about the culture of an economic 

 plant.— {Nature, October, 11th, 1900.) 



