Thomas Graham was a Scottish chemist. He was born in 1805 at Glasgow and died in 1869. Educated at Glasgow and Edinburgh, in 1827 he commenced teaching private mathematical classes in Glasgow, and in 1829 succeeded to the lectureship of chemistry in the Mechanics' Institution. 1830 he was appointed professor of chemistry in the Andersonian University. In 1831 he established the law that gases tend to diffuse inversely as the square root of their specific gravities. He afterwards made a series of investigations into the constitution of ar-seniates, phosphates, and phosphoretted hydrogen, and into the function of water in different salts.
In 1837 he was appointed professor of chemistry at University College, London, , and soon after settling in the metropolis he was appointed assayer to the mint, holding the post at University College until 1855 when he became master of the Mint. Thomas Graham was the first president of the Chemical Society, founded in 1841.
In 1846 he assisted in founding the Cavendish Society, over which be presided. He read the Bakerian lecture in 1849 and in 1854, the subject of both being the diffusion of liquids, which he further treated before the Eoyal Society in 1861. He distinguished the crystalloids and colloids in liquid solutions, and gave to their separation the name of dialysis, In a subsequent paper, Philosophical Transactions, 1866, he applied these discoveries to gases, under the name of atmolysis. The passage of gases through heated metal plates and the occlusion of gases were also ably investigated by him. Research Thomas Graham
Atherosclerosis is a form of arteriosclerosis. Atherosclerosis is the hardening of the arteries caused by cholesterol plaque deposits. It can occur in the coronary arteries, the carotid arteries, the aorta, and the leg arteries. Healthy arteries are flexible, strong, and elastic. The inner layer, the tunica interna, is smooth, enabling blood to flow freely. As a person ages, the arteries normally become thicker and less elastic, and their calcium content increases. This natural ' hardening' process occurs throughout the artery system.
Atherosclerosis, by contrast, affects only the larger arteries. As the plaque builds up, the inner layers of the artery walls become thick and irregular. Fat, cholesterol, and other materials accumulate in certain areas. This gradual build-up over a long period of time reduced the circulation of blood and increases the risk of heartattack, stroke, and other serious arterial diseases. A person having atherosclerosis will often experience symptoms of angina, stroke, and claudication. All of the symptoms are caused by insufficient blood flow due to atherosclerosis. Initially, the deposits of fat-containing cells that lead to atherosclerosis are only slight streaks, and are called fatty streaks. As the fatty streaks enlarge, they invade the deeper layers of the artery walls, causing scarring and calcium deposits. Large deposits are called athermas or plaques. The plaques calcify into a chalky substance. The plaque consists of a firm shell that contains calcium with areas of fatty material, and a centre consisting of soft cholesterol. As the plaque deposits grow the cardiac muscle beyond the blockage becomes deprived of blood, a condition known as myocardial ischemia. The healthy elastic wall of the artery changes into dead and unresponsive scartissue. If insufficient blood flow continues, the cardiac muscle dies, causing myocardial infarction. As the degeneration of the endothelial lining of the arteries continues, the lining may be damaged. Bloodplatelets stick to the site of injury, and a chemical signal is activated that promotes an influx of cholesterol.
The symptoms of atherosclerosis develop slowly as the development of the occlusion of the arteries progresses. Symptoms include angina, stroke, and claudication. The specific symptoms depend on which artery or arteries are occluded. If the leg arteries are affected, symptoms usually include numbness, fatigue, or pain in the leg. Occlusion of the coronary arteries may lead to angina or even a heartattack. When atherosclerosis occurs in the coronary arteries, it can lead to myocardial ischemia, an insufficient flow of blood to the heart. If the duration of ischemia is brief, the damage is reversible. However, if the duration of ischemia is longer than 40 to 60 minutes, irreversible damage may occur, and the parts of the heart muscle deprived of blood become permanently damaged, leading to myocardial infarction. Other commonly affected large arteries include the carotid arteries and the abdominal aorta. Initially, the symptoms of atherosclerosis are more likely to occur during exercise or strenuous activity than at rest. The symptoms develop during exercise because the arteries cannot supply the muscles with enough oxygen and nutrients. This process results in the build-up of by-products in the muscle that cannot be removed efficiently because of the occluded blood flow. This build-up of waste products, such as lactic acid, causes pain. It is similar to the build-up of lactic acid in muscles due to overexertion. As the narrowing of the arteries increases, the symptoms become prevalent with less and less exertion. The symptoms generally disappear after a few minutes of rest. However, the occlusion can be so severe that even the resting muscle does not get enough blood flow and the symptoms may be experienced even when sitting still. Research Atherosclerosis
The basilar artery is a single artery located at the base of the skull. It is formed by the junction of two vertebral arteries. It supplies blood to the internal ear and parts of the brain. The basilar plexus is a network of small arteries between the layers of membrane that protect the brain (the dura mater) over the base of the skull. Blockage, or occlusion, of the basilar artery causes many serious problems, ranging from blindness to paralysis. Research Basilar Posterior Cerebral Artery
The cerebellar arteries supply the part of the brain located at the base of the skull behind the brain stem, the cerebellum. Blockage, or occlusion, of one of the arteries leading to the cerebellum may result in the loss of awareness of pain and temperature, numbness of the face, and paralysis or lack of coordination on one side of the body. Research Cerebellar Arteries
A tourniquet is a bandage or piece of rubber tubing used for stopping the flow of blood through a part of the body, generally a limb. Owing to the fact that the main arteries for the limbs are for the most part surrounded by muscle, any attempt to compress them with a tourniquet must involve: (a) A very tight constricting force. (b) Simultaneous compression of muscles and nerves. (c) Complete ischaemia (bloodlessness) of all the tissues beyond the point of application of the tourniquet. Risks of applying a tourniquet are therefore: 1. Insufficient compression of the artery but occlusion of the vein only, leading to congestion and increased bleeding from the ends of the cut veins. 2. Peripheral nerve injury and subsequent paralysis. 3. If the tourniquet remains in position too long, ischaemia and damage to muscles resulting in their contracture. 4. Damage to the artery wall, especially if it is already affected by arterio-sclerosis. Subsequent arterial thrombosis may occur.
In severe injuries where there has been considerable muscle damage, there is one distinct advantage in the application of a tourniquet. It prevents the return to the circulation of the histamine products of tissue damage, and as long as a tourniquet is in position there is less likelihood of severe surgical (secondary) oligaemic shock. Immediately the tourniquet is removed however, these substances reach the general circulation and the onset of oligaemic shock may be very rapid. In operations upon the limbs, a surgeon is able to work in a bloodless field by means of a suitably applied tourniquet. Research Tourniquet
Occlusion is the property possessed by certain solids, notably some metals, of retaining gases either within the solid or on the surface. There is no chemical combination in the accepted sense. Research Occlusion
A solution is a homogeneous mixture of substances that cannot be separated by mechanical means.
The commonest forms of solutions are liquid. Gases dissolve in liquids according to Henry's Law, which states that the mass of any gas absorbed by a liquid is proportional to the pressure of the gas, and decreases as the temperature increases. The law only applies to gases which have a low solubility. With high solubility the probability is that a chemical action takes place which apparently invalidates the law. The decrease of solubility with pressure is seen in the familiar example of opening a bottle of fizzy drink, the dissolved gases immediately beginning to bubble out from the liquid.
Liquids mix according to no well-defined law, but the mixing is important, as upon it depend the fractional distillation processes.
As a general rule, solids dissolve in liquids at a rate depending upon the temperature, but the rule has a number of notable exceptions, e.g.: solubility actually decreases with increase of temperature. Salt dissolves very little more in hot water than cold, while potassium nitrate dissolves nearly twenty times more in boiling water than in water at freezing point. When a liquid has dissolved as much of the solid as possible it is said to be saturated. A solid dissolves out from a saturated solution on cooling, as a rule, and generally in the form of crystals.
Solid solutions are of two kinds, the solution of gases in solids and the solution of solids in solids. The occlusion of hydrogen in palladium is a well-known example of the former, and amorphous mixtures of gases, of the latter.
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