BY DR. LAUDER BRUNTON. 449 



a test-tube, with glacial phosphoric acid or acid potassium 

 sulphate, and heat. The glycerin will be decomposed, and yield 

 uatcr and acrolein or acrol, a body which has an extremely 

 unpleasant smell, and causes great irritation of the nose and 

 eyes. 



Test for Glycerin. As no other body j'ields acrolein when 

 decomposed in the way just mentioned, its formation serves as 

 a test for glycerin ; and as it is very pungent, small quantities 

 of glycerin can easily be detected. 



55. Muscle. For the structure of muscle, see Chap. IY. 

 Reaction. Muscles which have been at rest have an amphi- 



cromatic reaction; i. e., they change red litmus to blue, and 

 also blue litmus to red. They do not alter the color of blue 

 litmus so much as that of red, and they are therefore alkaline. 

 Alteration in the Reaction by Contraction. The reaction 

 changes to acid after contraction of the muscle or after death. 

 See Chap. XX., Obs. VI. 



56. Composition of Muscle. The Sarcolemma is 

 usually said to agree with elastic tissue in its characters, and 

 to yield no gelatin, but it has been recently stated to be solu- 

 ble, though slowly, in alkalies and acids, as well as in gastric 

 juice, and would thus more nearly resemble connective tissue. 



57. Sarcous Elements. Little is known regarding the 

 chemical composition of the sarcous elements, except that 

 they swell slightly, and lose their power of double refraction 

 when boiled or when heated with alkalies or very dilute acids. 

 Alcohol does not alter them. 



f 58. Muscle Plasma. When muscles are subjected to 

 pressure at C., a fluid termed muscle plasma is obtained. 

 The plasma of muscles resembles the plasma of the blood, in 

 possessing the power of coagulating spontaneously, and sepa- 

 rating into a clot, and serum. To this clot, corresponding to 

 the fibrin of the blood, the name myosin has been given. Co- 

 agulation of the plasma causes the muscles to lose their elas- 

 ticity and become stiff and hard, and thus gives rise to rigor 

 mortis. After some time, decomposition sets in, and the mus- 

 cles again become soft and flexible. Muscle plasma is some- 

 what troublesome to obtain, as it coagulates too quickly in the 

 muscles of warm-blooded animals to allow of its preparation 

 from them, and the muscles of frogs, in which it coagulates 

 more slowh', are not always to be had in sufficient quantity. 



r reparation. Prepare a freezing mixture by mixing to- 

 gether equal parts of salt and snow, or pounded ice. Intro- 

 duce it into a large beaker, and plunge a platinum crucible or 

 small tin box into it. Fill another beaker with half per cent, 

 salt solution, and put it in a vessel containing snow or ice. 

 Prepare several frogs in the following manner: Open the thorax, 

 cut oil' the apex of the heart, push a canula up into the aortic 

 29 



