Pethybriuge and Murphy — Bacterial Disease of the Potato. 31 



that found in our case. We were unfortunately unable to obtain a copy of 

 the detailed characters of B. airosepticus before our own work was concluded. 

 Hence we were not able to make a comparative study of the behaviour of our 

 organism and that of van Hall in many of the media which he used ; but 

 sufficient has been done to show that the organisms are not identical. There 

 are even greater differences between our organism and B. solanisaprtcs. The 

 latter possesses far more flagella, forms no gas in glucose and cane-sugar 

 cultures, forms a distinct ring on the surface of potato-juice, and produces a 

 raised, creamy-white growth on cooked potato, all of which characters serve to 

 distinguish it from our organism. Between B. phytophthorus and the organism 

 isolated by us, however, there exist marked resemblances, so much so that we 

 are strongly tempted to regard the latter as probably only a variety of the 

 former. iSTevertheless there are certain differences which, if slight, are yet 

 quite constant, as repeated tests have convinced us. Thus in Appel's sterile 

 potato-juice, we have never been able to obtain the slightest signs of a 

 pellicle ; whereas B. phytophthorus produces a strong one. Again, in nitrate 

 broth we find that our organism produces a small amount of gas, while tliis ifi 

 apparently not the case with B. phytophthorus. Further, the growth in milk 

 is dissimilar in the two cases. Our organism causes the separation of the 

 curd as a not very compact mass, and produces a distinct acidity iu a 

 comparatively short time, whereas B. phytophthorus causes milk to change 

 only on long standing, forming then a compact cylinder of precipitated curd 

 and giving a reaction which is amphoteric to Ktmus. Evidently, however^ 

 the two organisms, if not identical, are at any rate closely allied ; and it is 

 perhaps with some reluctance that we regard it as a distinct species, and 

 suggest the name of Bacillus melanogenes for it. 



A careful comparison has also been made, as far as circumstances permitted, 

 between our organism and a group of organisms which have been recently 

 submitted to a long series of comparative studies by Harding and Morse (17), 

 and which have been described by various authors as causing a soft rot in 

 many fleshy vegetables of the North Temperate Zone, and of which Bacillus 

 carotovorus Jones serves as a type. The pathogenicity of B. carotovorus and 

 its allies towards potatoes is, as far as we are aware, not known ; hence a 

 comparison on tliis \ital point cannot be made. B. carotovorus produces 

 indol, though in feeble amount. B. melanogems does not do so at all. 

 B. carotovorus produces a white growth on cooked potato, B. melanogoies a 

 distinctly yeUow one. B. carotovorus has up to ten flagella; in B. melanogenes 

 we have never seen more than five. These differences are quite sufficient to 

 show that the organism obtained by us is not identical with B. carotovorus and 

 its allies. 



