Page:The American Cyclopædia (1879) Volume VI.djvu/699

EPIPHYTES 687 grow upon the outside, where there can be no warmth, others within the heated cavities of the body; some thrive best in light and pure air, others in darkness and carbonic acid ; some live in fluid, while others are always found dry. It will be seen then that all these points must be taken into consideration before we attempt to destroy them, and a universal parasite killer is an impossibility, for what is death to one species may be the food of another. The effect of their presence on man is as various as that of the animal parasites, though less dangerous. When the plant has found its favorite and essential elements for reproduction, it grows at once, be it on the outer surface or within the body. At first the growth may be merely su- perficial ; but soon the vegetative structure, the mycelium, begins to seek nourishment in deeper soil, and its filaments penetrate all tis- sues, wherever the minutest opening is left for its entrance. The spores or mycelium, by act- ing as a foreign body, may produce absorption in adjacent parts, and thus make way for their progress inward indefinitely. When once the spores gain admission we may see the same re- sult as when we plant the seeds of larger vege- tables in the soil. They send forth their sprouts upward and downward, pushing before them whatever resists their progress. But if in ad- dition to the sprouts we should have our seed increasing by self-division, and to an immense extent, what would follow? What wonder then if this process, carried on beneath the less yielding skin, should lead to inflammation and destruction of the parts ? The oidium albicans may become dangerous in an infant by ob- structing the oesophagus or glottis. Impaired vision may be caused by the growth of a fungus within the eye. Atrophy and deformity may result from their presence in the hair and nails. Erosions of the skin, and the inflammation they create, may bring on swelling of glands. Para- sites may also prove injurious by irritating the nervous system, as in pity- riasis versicolor, or chem- ically. The vinous fermen- tation is brought about by the action of a fungus on sugar, by which it is re- solved into carbonic acid and alcohol. So too the sarcina ventriculi and the oidium albicans may cause the acetous and lactic acid fermentations respective- ly. The very decay of ve- getable parasites may produce putridity in their masses. We see then that vegetable parasites are able to work a multitude of evils upon mankind, but the extent thereof must be in proportion to the condition and size of the organ affected. Although they may in some instances be as troublesome, as dangerous to life even, as their animal relatives, still we are not so much shocked to have our head covered with the sporules of the favus plant 300 VOL. vi. 44 yriasis versicolor. as with pediculi, though both are marks of un- cleanliness, or to know that our stomach is filled with sarcina, as to suspect that a frightful strongylus lies coiled up in our kidney. Fungi consist of organs of fructification and a nutri- tive apparatus. . This last is called mycelium, and is made up of threadlike, more or less compacted, elongated cells, which interlace and have no intimate connection. It has such an indefinite form, and diifers so little in various species, that from it alone we cannot distin- guish them. It varies greatly also according to the condition in which it grows, and whe- ther it be viewed damp or dry. It may exist without bearing fruit, as a tree may remain barren in uncongenial soil ; but no species can exist without it, though it may be reduced to a very low development when compared with the fruit-bearing system. Subtile forms of my- celium have the power of penetrating to remote parts, and lying dormant for a long time. The reproductive system consists of spores, which are very small, and in some species are enclosed in receptacles. Their number is literally in- calculable, and they increase with immense ra- pidity. They float freely in water, and their walls are very strong, so that they are well cal- culated to travel far from their birthplace. Their diminutive size enables them to gain ad- mission into the smallest crevices of the skin or elsewhere, and they are capable of with- standing great extremes of temperature, so that after being kept in a dry state for a long time they are found to possess their entire pristine vitality. The whole plan of their development is still little known, and there is good reason to believe that many of them are imperfectly devel- oped states of other plants, which, if they at- tained their proper sphere, might present a more complex structure; and when we con- sider the vast number of forms into which a single germ may develop itself according to the soil in which it happens to grow, their real number may be regarded as comparatively small, and this view is adopted by some emi- nent dermatologists. Some prey directly upon living tissues, while others destroy them first and induce decomposition, before the proper conditions for their development are attained. The fact of possible inoculation on healthy sub- jects proves that the presence of some forms at least is the essential cause of the disease con- nected with them. The fact that mycelium may exist for a long time dormant, till proper con- ditions are provided for its further development, will explain the sudden appearance of a fungus in various peculiar situations. In the potato disease, for instance, the lotrytis infestans may show itself in a few hours on the freshly cut surface of a tuber, and on microscopic exami- nation we find mycelium traversing the cells in all directions. They grow within nuts and egg shells, in the cavities of tomatoes when no lesion of the walls exists, and are developed within the brains of birds, in the eye and blad- der of man, and on globules of milk within the