Imágenes de páginas

Not only does this great world of organisms, hovering unseen about us, bristle with enemies to man and his friends, the domestic plants and animals, but among these enemies are numerous active, friendly species, contributing much to our wealth and comfort. . Thus, vinegar, one of our most important condiments, is made only through the agency of the acetic ferment; alcohol, a source of fearful iujury from its misuse, yet invaluable in science and the arts, is made by the action of the yeasts; clover, the hope of the despairing farmer, owes its soil-enriching power to a humble parasitic bacterium which seizes its roots for a home; and the finer flavors of the most aromatic butter are traced to the products of the action of particular species of bacteria in the ripening cream.


Turning now to the consideration of the influence of bacteria in tobacco culture, we omit all reference to the fungous diseases to which the growing plant is subject, and confine attention to the relations of these organisms to the processes of curing and sweating. As the result of these processes, instead of the green color, rough, hard surface, brittle web, black ash, dark, tarry, ill-smelling smoke and bitter, burning flavor possessed by a quickly dried tobacco leaf, the leaves have a beautiful brown color, silky texture, elastic web, light blue and pleasantly aromatic smoke, a white or gray ash, and little of the unpleasant flavor of the green leaf.

A very large fraction of these changes in quality is wrought during the first of these processes, the curing. Despite the fact that the Germans term it das Trocknen, or drying, it is neither a simple physical process, nor a purely chemical one. The results of late studies by Miiller-Thurgau * and Dr. J. Behrens, f show tnat dur

• Laixlwirthsohaftltohes Jnhrbuch, 14, 485-512.
tLantlwirtbscharUiche Versuchs-Staiiunen, 43, 280-8KI.

ing the process there is a large decrease in the dry matter of the leaf, as well as in the water. The starch is turned to glucose, and the latter passes back into the veins, midrib and stem, and is finally destroyed there and breathed off r% carbonic acid gas and water, owing to an abnormally increased respiration. There is no loss of nitrogen, either in the form of nicotine, nitric acid or albuminoids; the latter compounds are, however, largely split up with the resultant formations of asparagine and other amides,—a change similar to that which occurs whenever leaves are for a long time shaded, or to that observed in the process of ensilage. Mere drying, and the slow oxidation caused by the direct action of the oxygen of the air, do not suffice to explain these changes. They are the result of life action.

It is not probable, though, that the lower organisms are important in the normal curing process. Behrens remarks,* "micro-organisms were not found in an active condition upon the curing leaves, and their development upon the surface of the leaves, the sole point open to their attack, is rendered well-nigh impossible, owing to its dryness, to say nothing of the general dry condition of the inner tissues."

The changes occur only while the protoplasm of the leaf cells retains life. If the leaf be frozen, or chloroformed, the protoplasm is killed, and no normal curing can be effected thereafter. Evidently, the changes observed during the curing are due to an abnormal action of the dying protoplasm of the leaves themselves; and bacterial aid offers no advantages.

During this process, however, the lower organisms sometimes act injuriously. "Pole-burn" is prevalent during warm, damp, foggy weather; in a few hours, the whole crop may be turned to a dark brown, wet,

•Loc. olt., p. 286.

soggy and easily torn lot of leaves, hopelessly damaged. Dr. Wm. 0. Sturgis,* in describing this disease, says: "It is characterized by the appearance on the surface of the leaf, of small blackened areas, giving the leaf the aspect of having been sprinkled with some corrosive liquid. . . . These areas increase in size, become confluent, and sometimes within thirty-six hours, or at most, fortyeight, not only is the whole leaf affected, but the entire contents of the curing barn may be rendered quite worthless as tobacco. Microscopic study revealed in the center of each blackened spot a minute, elevated pustule. Sections through the center of one of these pustules showed that the tissue of the leaf was largely disintegrated, and the cells themselves were largely filled with bacteria. . . . They develop rapidly in the tissues of the leaf, raising the epidermis, and finally breaking through at one or more points in the blackened area, . . . they spread out in a thin, slimy film, . . . forming a brown, translucent crust of cheesy consistency, and composed entirely of the bacteria themselves."

In tracing the development of the disease, this author states that, at first, the surface of the leaf is attacked by a fungus of the genus Cladosporium, related to the leaf-spot disease of the tomato. This does little direct injury, but after some time the leaf is attacked by the bacteria, which swarm into the interior through the breaches made by the Cladosporium, the remains of which are found mingled with the bacteria. Of the latter, there are, at least, two species, one a true Bacterium, the other a Micrococcus, of the variety Streptococcus.

These bacteria develop best between 70° and 90° F., but a temperature above 90° to 110°, or below 35° to 40°, checks their development. Furthermore, all attempts to inoculate the cured tobacco with them failed; the

"report of the Connecticut A.g. Exp. Sta., 1891, pp. 168-186.

crop is in little danger after a period varying from ten to twenty days after the beginning of curing. The remedy suggested is free ventilation and control of temperature by aid of artificial heat.

Behrens,* in a similar study, found instead of a Cladosporium, Botrytis cinerea P., a spore-bearing fungus, and Sclerotinia Libertiana, Fckl., acting as the forerunners of decay, while others f have noted Pleospora sp., Botrytis vulgaris, Fr., and two species of the genus Mur.or as thus active.

Another disease to which curing tobacco is also subject, is "stem rot," or white vein. This often attacks the stalk a few days after cutting, but sometimes appears, late in the curing, upon imperfectly dried ribs and veins. These parts of the leaf are covered with patches of a long-piled, velvety mold of pure white color. Later, the web of the leaf is often invaded. These white patches are the mycelium of a species belonging to the genus Botrytis; the threads of the mycelium, first attacking the surface, later penetrate deeply into the underlying tissues. From the mycelial threads spring erect fibers, one-fourth of an inch high, giving the velvety appearance. These erect stems bear branches, extending at right angles, and at the tips of these branches are formed the reproducing spores. This advanced suite of development is rarely reached on the curing tobacco, because the time is too short and the moisture insufficient The formation of spores occurs in the stems and rib after the stripping, and often the fungus springs up over the floor of the curing barn, and the next crop of leaf hung in the building will be in danger of inoculation by means of the spores developed by this growth of the fungus. The remedies suggested by Sturgist are

•Zeitschrlft flir Pflanzenkrankhelten, 3. p. 82.

tSturgis, Report of the Connecticut Agricultural Experiment Station, 1893, p. 85.

I Report of the Connecticut Agricultural Ex. St a., 1891, p. 186.

the burning of all infected waste material from an old crop; the thorough fumigation of the curing barn, by burning sulphur after the removal of the crop, and again two weeks before the introduction of the new crop; the sprinkling of the floor with a mixture of equal parts of dry air-slaked lime and sulphur; or even tlu covering of the earthen floor with an inch of clean soil.


While the curing of the tobacco is, in all probability, the effect of modified activity of the leaf cells themselves, the same cannot be said of the sweating. At the close of the curing process the leaves are fully dead. If the leaves be remoistened, packed closely together and allowed to stand, an action sets up, liberating heat and introducing new qualities into the tobacco. Nessler * was the first to explicitly declare that the process was distinctly a fermentative one; although Rollerf notes the addition of yeast to promote the rapidity of the action, implying a more or less clear recognition of the analogy between this process and alcoholic fermentation.

At the time Nessler wrote, the principles and methods of bacteriological research were unknown, so that his reasoning from analogy could not be submitted to direct proof by experiment. Since then, however, a number of interesting researches have been made. Of these, one of the earlier is that of Th. Schloesing J upon the fermentations of tobacco used for the preparation of snuff. Work by the elder Schloesing had shown that there was a heavy consumption of atmospheric oxygen by the fermenting tobacco. Th. Schloesing set out to ascertain whether this was due to a purely chemical change, or whether bacterial action was wholly or par

* Der Tabak, 1867, pp. 122-136.

1 Der Tiibuk, Augsburg, 1808, p. 75.

J Memorial de* manufactures de I'4tat. Vol. I, Part 4, pp. 614-51M; Vol. II, Part 1, pp. 119-136; Part 2, pp. 1U2-210.

« AnteriorContinuar »