6O BACTERIA IN RELATION TO PLANT DISEASES. 



LUMINOSITY. 



Numerous saprophytic bacteria are luminous under certain special conditions. 

 Luminosity is also a striking characteristic of at least one bacterial animal disease 

 the white disease, or sluggish disease, of sand fleas ( Talorchestia longicornis and T. 

 megalophthalmid), common on the shores of France and ot Massachusetts at Woods 

 Hole. Decaying potatoes and other vegetables are sometimes luminous. The 

 question of luminosity should therefore be kept in mind by the student of plant 

 diseases, although no luminous species are known to live in plants. Most of 

 these interesting luminous bacteria have been found in salt water or near it, or on 

 the flesh of quadrupeds and fish. Gorham has been able to grow them on strictly 

 synthetic media. The most recent treatise is by Hans Molisch (Leuchtende 

 Pflanzen, Jena, Gustav Fischer, 1904, pp. ix, 169, with 2 plates and 16 text figures). 



Molisch records 26 species of luminous bacteria. He found that salt-water fish 

 and the flesh of cattle exposed in the markets were very often luminous 48 per 

 cent of 70 samples of the latter and nearly all the former. Of horse flesh 65 per cent 

 and of cattle flesh 89 per cent became luminous on putting it into 3 per cent solution 

 of sodium chloride, allowing a part of it to project into the air. Fresh-water fish 

 are very seldom luminous. Seedlings exposed to Petri-dish poured plates curved 

 heliotropically toward the light, but they did not become green. Other chlorides 

 than that of sodium stimulate growth and light-production, e, g., potassium, 

 magnesium, or calcium chloride. Certain non-chlorides, such as potassium iodide, 

 potassium sulfate, and magnesium sulfate have the same action (3 per cent or less). 

 Potassium nitrate was also active on B. phosphoreum but not on B. phologenus. 

 Manganese sulfate stimulated growth very noticeably but had no corresponding effect 

 on- the luminosity, which was weak. The spectrum of B. phosphoreum differs from 

 that of the West Indian beetle, Pyrophorus noctilucus, and from that of a luminous 

 fungus known as mycelium X. No biological importance is attributed to the 

 luminosity which is ascribed to an hypothetical phologen. It is an oxidization 

 phenomenon which can take place only in the presence of free oxygen. A tem- 

 perature of 30 C. for forty-eight hours is sufficient to kill B. phosphoreum in gelatin 

 cultures. The minimum temperature for this organism is below zero, the optimum 

 is about 16 to 18 C., and the maximum is 28 C. The bacteria are luminous 

 from minus 5 to plus 28 C. Light production is most intense from 5 to 20 C. 



FERMENTATION PRODUCTS. 



The old conception of fermentation involves an evolution of gas (fervere, to 

 boil), but the term is now used with a wider meaning. Like many other terms, it is 

 difficult to use it always logically. In general, it means the breaking up of carbon 

 compounds into simpler substances, either by the direct action of the protoplasm of 

 the organism (hypothetical) or by chemical substances (enzyms, diastases) secreted 

 by the protoplasm. Acids and alcohols are produced ; gases may or may not be 

 evolved. Other volatile products are also produced, e. g., esters, but usually only 

 in very small quantities. Certain of the bacterial fermentations are of large com- 

 mercial importance, e. g., the acetic, the lactic. The breaking up of albumen and 



