DIABASE

diabase, in petrology, a rock which is a weathered form of dolerite. it was long widely accepted that the pre-tertiary rocks of this group differed from their tertiary and recent representatives in certain essential respects, but this is now admitted to be untenable, and the differences are known to be merely the result of the longer exposure to decomposition, pressure and shearing, which the older rocks have experienced. their olivine tends to become serpentinized; their augite changes to chlorite and uralite; their felspars are clouded by formation of zeolites, calcite, sericite and epidote. the rocks acquire a green colour (from the development of chlorite, uralite and epidote); hence the older name of "greenstones," which is now little used. many of them become somewhat schistose from pressure ("greenstone-schists," meta-diabase, &c.). although the original definition of the group can no longer be justified, the name is so well established in current usage that it can hardly be discarded. the terms diabase and dolerite are employed really to designate distinct facies of the same set of rocks. the minerals of diabase are the same as those of dolerite, viz. olivine, augite, and plagioclase felspar, with subordinate quantities of hornblende, biotite, iron oxides and apatite. there are olivine-diabases and diabases without olivine; quartz-diabases, analcite-diabases (or teschenites) and hornblende diabases (or proterobases). hypersthene (or bronzite) is characteristic of another group. many of them are ophitic, especially those which contain olivine, but others are intersertal, like the intersertal dolerites. the last include most quartz-diabases, hypersthene-diabases and the rocks which have been described as tholeites. porphyritic structure appears in the diabase-porphyrites, some of which are highly vesicular and contain remains of an abundant fine-grained or partly glassy ground-mass (_diabas-mandelstein_, amygdaloidal diabase). the somewhat ill-defined spilites are regarded by many as modifications of diabase-porphyrite. in the intersertal and porphyrite diabases, fresh or devitrified glassy base is not infrequent. it is especially conspicuous in some tholeites (hyalo-tholeites) and in weisselbergites. these rocks consist of augite and plagioclase, with little or no olivine, on a brown, vitreous, interstitial matrix. devitrified forms of tachylyte (sordawilite, &c.) occur at the rapidly chilled margins of dolerite sills and dikes, and fine-grained spotted rocks with large spherulites of grey or greenish felspar, and branching growths of brownish-green augite (variolites). to nearly every variety in composition and structure presented by the diabases, a counterpart can be found among the tertiary dolerites. in the older rocks, however, certain minerals are more common than in the newer. hornblende, mostly of pale green colours and somewhat fibrous habit, is very frequent in diabase; it is in most cases secondary after pyroxene, and is then known as uralite; often it forms pseudomorphs which retain the shape of the original augite. where diabases have been crushed or sheared, hornblende readily develops at the expense of pyroxene, sometimes replacing it completely. in the later stages of alteration the amphibole becomes compact and well crystallized; the rocks consist of green hornblende and plagioclase felspar, and are then generally known as epidiorites or amphibolites. at the same time a schistose structure is produced. but transition forms are very common, having more or less of the augite remaining, surrounded by newly formed hornblende which at first is rather fibrous and tends to spread outwards through the surrounding felspar. chlorite also is abundant both in sheared and unsheared diabases, and with it calcite may make its appearance, or the lime set free from the augite may combine with the titanium of the iron oxide and with silica to form incrustations or borders of sphene around the original crystals of ilmenite. epidote is another secondary lime-bearing mineral which results from the decomposition of the soda lime felspars and the pyroxenes. many diabases, especially those of the teschenite sub-group, are filled with zeolites. diabases are exceedingly abundant among the older rocks of all parts of the globe. popular names for them are "whinstone," "greenstone," "toadstone" and "trap." they form excellent road-mending stones and are much quarried for this purpose, being tough, durable and resistant to wear, so long as they are not extremely decomposed. many of them are to be preferred to the fresher dolerites as being less brittle. the quality of the cornish greenstones appears to have been distinctly improved by a smaller amount of recrystallization where they have been heated by contact with intrusive masses of granite. (j. s. f.) diabetes (from gr. [greek: dia], through, and [greek: bainein], to pass), a constitutional disease characterized by a habitually excessive discharge of urine. two forms of this complaint are described, viz. diabetes mellitus, or glycosuria, where the urine is not only increased in quantity, but persistently contains a greater or less amount of sugar, and diabetes insipidus, or polyuria, where the urine is simply increased in quantity, and contains no abnormal ingredient. this latter, however, must be distinguished from the polyuria due to chronic granular kidney, lardaceous disease of the kidney, and also occurring in certain cases of hysteria. _diabetes mellitus_ is the disease to which the term is most commonly applied, and is by far the more serious and important ailment. it is one of the diseases due to altered metabolism (see metabolic diseases). it is markedly hereditary, much more prevalent in towns and especially modern city life than in more primitive rustic communities, and most common among the jews. the excessive use of sugar as a food is usually considered one cause of the disease, and obesity is supposed to favour its occurrence, but many observers consider that the obesity so often met with among diabetics is due to the same cause as the disease itself. no age is exempt, but it occurs most commonly in the fifth decade of life. it attacks males twice as frequently as females, and fair more frequently than dark people. the symptoms are usually gradual in their onset, and the patient may suffer for a length of time before he thinks it necessary to apply for medical aid. the first symptoms which attract attention are failure of strength, and emaciation, along with great thirst and an increased amount and frequent passage of urine. from the normal quantity of from 2 to 3 pints in the 24 hours it may be increased to 10, 20 or 30 pints, or even more. it is usually of pale colour, and of thicker consistence than normal urine, possesses a decidedly sweet taste, and is of high specific gravity (1030 to 1050). it frequently gives rise to considerable irritation of the urinary passages. by simple evaporation crystals of sugar may be obtained from diabetic urine, which also yields the characteristic chemical tests of sugar, while the amount of this substance can be accurately estimated by certain analytical processes. the quantity of sugar passed may vary from a few ounces to two or more pounds per diem, and it is found to be markedly increased after saccharine or starchy food has been taken. sugar may also be found in the blood, saliva, tears, and in almost all the excretions of persons suffering from this disease. one of the most distressing symptoms is intense thirst, which the patient is constantly seeking to allay, the quantity of liquid consumed being in general enormous, and there is usually, but not invariably, a voracious appetite. the mouth is always parched, and a faint, sweetish odour may be evolved from the breath. the effect of the disease upon the general health is very marked, and the patient becomes more and more emaciated. he suffers from increasing muscular weakness, the temperature of his body is lowered, and the skin is dry and harsh. there is often a peculiar flush on the face, not limited to the malar eminences, but extending up to the roots of the hair. the teeth are loosened or decay, there is a tendency to bleeding from the gums, while dyspeptic symptoms, constipation and loss of sexual power are common accompaniments. there is in general great mental depression or irritability. diabetes as a rule advances comparatively slowly except in the case of young persons, in whom its progress is apt to be rapid. the complications of the disease are many and serious. it may cause impaired vision by weakening the muscles of accommodation, or by lessening the sensitiveness of the retina to light. also cataract is very common. skin affections of all kinds may occur and prove very intractable. boils, carbuncles, cellulitis and gangrene are all apt to occur as life advances, though gangrene is much more frequent in men than in women. diabetics are especially liable to phthisis and pneumonia, and gangrene of the lungs may set in if the patient survives the crisis in the latter disease. digestive troubles of all kinds, kidney diseases and heart failure due to fatty heart are all of common occurrence. also patients seem curiously susceptible to the poison of enteric fever, though the attack usually runs a mild course. the sugar temporarily disappears during the fever. but the most serious complication of all is known as diabetic coma, which is very commonly the final cause of death. the onset is often insidious, but may be indicated by loss of appetite, a rapid fall in the quantity of both urine and sugar, and by either constipation or diarrhoea. more rarely there is most acute abdominal pain. at first the condition is rather that of collapse than true coma, though later the patient is absolutely comatose. the patient suffers from a peculiar kind of dyspnoea, and the breath and skin have a sweet ethereal odour. the condition may last from twenty-four hours to three days, but is almost invariably the precursor of death. diabetes is a very fatal form of disease, recovery being exceedingly rare. over 50% die of coma, another 25% of phthisis or pneumonia, and the remainder of bright's disease, cerebral haemorrhage, gangrene, &c. the most favourable cases are those in which the patient is advanced in years, those in which it is associated with obesity or gout, and where the social conditions are favourable. a few cures have been recorded in which the disease supervened after some acute illness. the unfavourable cases are those in which there is a family history of the disease and in which the patient is young. nevertheless much may be done by appropriate treatment to mitigate the severity of the symptoms and to prolong life. there are two distinct lines of treatment, that of diet and that of drugs, but each must be modified and determined entirely by the idiosyncrasy of the patient, which varies in this condition between very wide limits. that of diet is of primary importance inasmuch as it has been proved beyond question that certain kinds of food have a powerful influence in aggravating the disease, more particularly those consisting largely of saccharine and starchy matter; and it may be stated generally that the various methods of treatment proposed aim at the elimination as far as possible of these constituents from the diet. hence it is recommended that such articles as bread, potatoes and all farinaceous foods, turnips, carrots, parsnips and most fruits should be avoided; while animal food and soups, green vegetables, cream, cheese, eggs, butter, and tea and coffee without sugar, may be taken with advantage. as a substitute for ordinary bread, which most persons find it difficult to do without for any length of time, bran bread, gluten bread and almond biscuits. a patient must never pass suddenly from an ordinary to a carbohydrate-free diet. any such sudden transition is extremely liable to bring on diabetic coma, and the change must be made quite gradually, one form of carbohydrate after another being taken out of the diet, whilst the effect on the quantity of sugar passed is being carefully noted meanwhile. the treatment may be begun by excluding potatoes, sugar and fruit, and only after several days is the bread to be replaced by some diabetic substitute. when the sugar excretion has been reduced to its lowest point, and maintained there for some time, a certain amount of carbohydrate may be cautiously allowed, the consequent effect on the glycosuria being estimated. the best diet can only be worked out experimentally for each individual patient. but in every case, if drowsiness or any symptom suggesting coma supervene, all restrictions must be withdrawn, and carbohydrate freely allowed. the question of alcohol is one which must be largely determined by the previous history of the patient, but a small quantity will help to make up the deficiencies of a diet poor in carbohydrate. scotch and irish whisky, and hollands gin, are usually free from sugar, and some of the light bordeaux wines contain very little. fat is beneficial, and can be given as cream, fat of meat and cod-liver oil. green vegetables are harmless, but the white stalks of cabbages and lettuces and also celery and endive yield sugar. laevulose can be assimilated up to 11⁄2 ozs. daily without increasing the glycosuria, and hence apples, cooked or raw, are allowable, as the sugar they contain is in this form. the question of milk is somewhat disputed; but it is usual to exclude it from the rigid diet, allowing a certain quantity when the diet is being extended. thirst is relieved by anything that relieves the polyuria. but hypodermic injections of pilocarpine stimulate the flow of saliva, and thus relieve the dryness of the mouth. constipation appears to increase the thirst, and must always be carefully guarded against. the best remedies are the aperient mineral waters. numerous medicinal substances have been employed in diabetes, but few of them are worthy of mention as possessed of any efficacy. opium is often found of great service, its administration being followed by marked amelioration in all the symptoms. morphia and codeia have a similar action. in the severest cases, however, these drugs appear to be of little or no use, and they certainly increase the constipation. heroin hydrochloride has been tried in their place, but this seems to have more power over slight than over severe cases. salicylate of sodium and aspirin are both very beneficial, causing a diminution in the sugar excretion without counterbalancing bad effects. in _diabetes insipidus_ there is constant thirst and an excessive flow of urine, which, however, is not found to contain any abnormal constituent. its effects upon the system are often similar to those of diabetes mellitus, except that they are much less marked, the disease being in general very slow in its progress. in some cases the health appears to suffer very slightly. it is rarely a direct cause of death, but from its debilitating effects may predispose to serious and fatal complications. it is best treated by tonics and generous diet. valerian has been found beneficial, the powdered root being given in 5-grain doses.