Page:EB1911 - Volume 02.djvu/207

This page has been proofread, but needs to be validated.
195
APOPHYGE—APOPLEXY

APOPHYGE (Gr. ἀποφυγή, a flying off), in architecture, the lowest part of the shaft of an Ionic or Corinthian column, or the highest member of its base if the column be considered as a whole. The apophyge is the inverted cavetto or concave sweep, on the upper edge of which the diminishing shaft rests.

APOPHYLLITE, a mineral often classed with the zeolites, since it behaves like these when heated before the blowpipe and has the same mode of occurrence; it differs, however, from the zeolites proper in containing no aluminium. It is a hydrous potassium and calcium silicate, H7KCa4(SiO3)8 + 4½(H2O). A small amount of fluorine is often present, and it is one of the few minerals in which ammonium has been detected. The temperature at which the water is expelled is higher than is usually the case with zeolites; none is given off below 200°, and only about half at 250°; this is slowly reabsorbed again from moist air, and is therefore regarded as water of crystallization, the remainder being water of constitution. When heated before the blowpipe, the mineral exfoliates, owing to loss of water, and on this account was named apophyllite by R. J. Haüy in 1806, from the Greek ἀπο, from, and φύλλον, a leaf.

1911 Britannica - Apophyllite.png
Fig. 1.Fig. 2.

Apophyllite always occurs as distinct crystals, which belong to the tetragonal system. The form is either a square prism terminated by the basal planes (fig. 2), or an acute pyramid (fig. 1). A prominent feature of the mineral is its perfect basal cleavage, on which the lustre is markedly pearly, presenting, in white crystals, somewhat the appearance of the eye of a fish after boiling, hence the old name fish-eye-stone or ichthyophthalmite for the mineral. On other surfaces the lustre is vitreous. The crystals are usually transparent and colourless, sometimes with a greenish or rose-red tint. Opaque white crystals of cubic habit have been called albine; xylochlore is an olive-green variety. The hardness is 4½, and the specific gravity 2.35.

The optical characters of the mineral are of special interest, and have been much studied. The sign of the double refraction may be either positive or negative, and some crystals are divided into optically biaxial sectors. The variety known as leucocyclite shows, when examined in convergent polarized light, a peculiar interference figure, the rings being alternately white and violet-black and not coloured as in a normal figure seen in white light.

Apophyllite is a mineral of secondary origin, commonly occurring, in association with other zeolites, in amygdaloidal cavities in basalt and melaphyre. Magnificent groups of greenish and colourless tabular crystals, the crystals several inches across, were found, with flesh-red stilbite, in the Deccan traps of the Western Gháts, near Bombay, during the construction of the Great Indian Peninsular railway. Groups of crystals of a beautiful pink colour have been found in the silver veins of Andreasberg in the Harz and of Guanaxuato in Mexico. Crystals of recent formation have been detected in the Roman remains at the hot springs of Plombières in France.  (L. J. S.) 

APOPHYSIS (Gr. ἀπόφυσις, offshoot), a bony protuberance, in human physiology; also a botanical term for the swelling of the spore-case in certain mosses.

APOPLEXY (Gr. ἀποπληξία, from ἀποπλήσσειν, to strike down, to stun), the term employed by Galen to designate the “sudden loss of feeling and movement of the whole body, with the exception of respiration,” to which, after the time of Harvey, was added “and with the exception of the circulation.” Although the term is occasionally employed in medicine with other significations, yet in its general acceptation apoplexy may be defined as a sudden loss of consciousness, of sensibility, and of movement without any essential modification of the respiratory and circulatory functions occasioned by some brain disease. It was discovered that the majority of the cases of apoplexy were due to cerebral haemorrhage, and what looked like cerebral haemorrhage, red softening; and the idea for a long time prevailed that apoplexy and cerebral haemorrhage could be employed as synonymous terms, and that an individual who, in popular parlance, “had an apoplectic stroke,” had necessarily suffered from haemorrhage into his brain. A small haemorrhage may not, however, cause an apoplectic fit, nor is an apoplectic fit always caused by haemorrhage; it may be due to sudden blocking of a large vessel by a clot from a distant part (embolism), or by a sudden clotting of the blood in the vessel itself (thrombosis). Owing to the prevailing idea in former times that cerebral haemorrhage and apoplexy were synonymous terms, the word apoplexy was applied to haemorrhage into other organs than the brain; thus the terms pulmonary apoplexy, retinal apoplexy and splenic apoplexy were used.

The term “apoplexy” is now used in clinical medicine to denote that form of coma or deep state of unconsciousness which is due to sudden disturbance of the cerebral circulation occasioned by a local cause within the cranial cavity, as distinct from the loss of consciousness due to sudden failure of the heart’s action (syncope) or the coma of narcotic or alcoholic poisoning, of status epilepticus, of uraemia or of head injury.

The sudden coma of sunstroke and heat-stroke might be included, although owing to the suddenness with which a person may be struck down, the term heat apoplexy is frequently used, and, from an etymological point of view, quite justifiably. The older writers use the term simple apoplexy for a sudden attack which could not be explained by any visible disease. Again, congestive apoplexy was applied to those cases of coma where, at the autopsy, nothing was found to account for the coma and death except engorgement of the vessels of the brain and its membranes. In senile dementia and in general paralysis the brain is shrunken and the convolutions atrophied, the increased space in the ventricles and between the convolutions being filled up with the cerebro-spinal fluid. In these diseases apoplectic states may arise, terminating fatally; the excess of fluid found in such cases was formerly thought to be the cause of the symptoms, consequently the condition was called serous apoplexy. Such terms are no longer used, owing to the better knowledge of the pathology of brain disease.

Having thus narrowed down the application of the term “apoplexy,” we are in a position to consider its chief features, and the mechanism by which it is produced. Apoplexy may be rapidly fatal, but it is very seldom instantly fatal. The onset is usually sudden, and sometimes the individual may be struck down in an instant, senseless and motionless, “warranting those epithets, which the ancients applied to the victims of this disease, of attoniti and siderati, as if they were thunder-stricken or planet-struck” (Sir Thomas Watson). The attack, however, may be less sudden and, not infrequently, attended by a convulsion; while occasionally, in the condition termed ingravescent apoplexy, the coma is gradual in its onset, occupying hours in its development. Although unexpected, various warning symptoms, sometimes slight, sometimes pronounced, occur in the majority of cases. Such are, fulness in the head, headache, giddiness, noises in the ears, mental confusion, slight lapses of consciousness, numbness or tingling in the limbs. A characteristic apoplectic attack presents the following phenomena: the individual falls down suddenly and lies without sense or motion, except that his pulse keeps beating and his breathing continues. He appears to be in a deep sleep, from which he cannot be roused; the breathing is laboured and stertorous, and is accompanied with puffing out of the cheeks; the pulse may be beating more strongly than natural, and the face is often flushed and turgid. The reflexes are abolished. Although apoplexy may occur without paralysis, and paralysis without apoplexy, the two, owning the same cause, very frequently co-exist, or happen in immediate sequence and connexion; consequently there is in most cases definite evidence of paralysis affecting usually one side of the body in addition to the coma. Thus the pupils are unequal; there may be asymmetry of the face, or the limbs may be more rigid or flaccid on one side than on the other. These signs of localized disease enable a distinction to be made from the coma