60 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 (Zalorchestia longicornis and T. 
megalophthalmia), 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. 1x, 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. photogenus. 
Manganese sulfate stimulated growth very noticeably but had no corresponding effect 
on the luminosity, which was weak. ‘The spectrum of 2. 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 photogen. 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 (/ervere, 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, é. g., the acetic, the lactic. The breaking up of albumen and 
aed 
