The growth of cholesterol monohydrate from solutions of bile salt,lecithin, and small electrolytes has been studied by microscopy and with the Coulter Counter. The crystal forms found by micocopy are the same as those seen in human gallstones and in squirrel monkey cholesterol microliths. The cholesterol growth rates determined with the Coulter Counter vary slowly with cholesterol concentration at low degree of supersaturation but become exponential at higher cholesterol concentrations. Growth is accelerated by the presence of calcium and magnesium but inhibited by potassium. These results can be combined with previous measurements of cholesterol dissolution rates to give a more accurate picture of the dynamics of gallstone formation. The complex nature of real bile, in which many factors may change from sample to sample, makes it difficult to study nucleation and growth systematically.
A Mathieu-type pendulum magnetic balance is described that employs the Faraday principle for measuring the specific magnetization of ferromagnetic materials. The balance can be operated automatically, or deflections may be read optically. The sensitivity of the balance can be varied twenty-fold by changing the weight distribution, and the calibration remains constant for years. Specific magnetizations are obtained with a precision of ±0.3%. Field strengths up to 10 000 oe can be held constant within ±0.3% for several hours. Specimens can be heated to 800°C or cooled to −180°C, and the temperature can be held constant to ±1.0°C for isothermal measurements. Automatic heating of the specimen at constant rate is provided.
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