320 PRACTICAL PHYSIOLOGY 



then removed and quickly passed through the mincing machine. 

 The mince is mixed with a 5 per cent, solution of magnesium sulphate, 

 the mixture being placed on ice and left standing all night. 



Divide some of the extract provided into two parts, a and b. 



EXPERIMENT I. (a) Dilute with four volumes of water, and place 

 in the waterbath at body temperature. A clot forms, leaving muscle 

 serum. 



(b) Add some acetic acid. A precipitate forms. Filter. Neutralise 

 the filtrate with Na 2 CO 3 solution, and dilute it with water. Place it in 

 the waterbath at 37 C., and note that no coagulum forms. 



These two experiments show us that the extract contains in solution 

 a substance which is precipitated by acetic acid, and which becomes 

 transformed into an insoluble clot under suitable conditions. This 

 body is protein in nature. Prove this by dissolving the clot in (a) in 

 10 per cent, sodium chloride and applying the protein tests. The 

 soluble body is called myosinogen, and the clot myosin. 



Besides myosinogen the extract contains, however, other proteins. 



EXPERIMENT II. Take some of the muscle serum in (a), or of the 

 nitrate in (6), and half saturate with ammonium sulphate. A pre- 

 cipitate of globulin results. Filter off this globulin and test the nitrate 

 for albumin by full saturation with (NH 4 ) 2 SO 4 , or by coagulation by 

 heat after faintly acidifying. 



EXPERIMENT III. Use the saline extract of muscle provided. 

 Heat 5 c.c. carefully in a test tube in the watevbath. Note the 

 temperature of the first signs of coagulation. Filter off coagulum and 

 heat the filtrate, noting the temperature at which the flocculi of a 

 second coagulum appear. It will be found that the first protein 

 (paramyosinogen, also termed myosin) is coagulated at 47 C. ; the 

 second protein (myosinogen, also called myogen) at 56 C. 



Both these bodies serve as the source of the coagulated myosin in 

 muscle. In the clotting associated with rigor mortis it is stated that 

 paramyosinogen is converted directly into myosin ; whereas myosinogen 

 is first converted into a soluble form (solub]e myosin), which is then 

 turned into insoluble myosin. Soluble myosin can be identified by its 

 low-heat coagulation point (40 C.). 



The coagulation points of the chief proteins of frog's muscle have 

 already been graphically studied. 



EXPERIMENT IV. Show that the watery extract of muscle provided 

 contains less protein than the saline extract. It contains albumin, but 

 not globulin. Demonstrate this fact. Coagulate the albumin by heat, 

 and save the filtrate to test for phosphates later. 



Organic Extractives. These are organic substances which are 

 soluble in water, but not protein in nature. They may be divided into 

 two classes, (a) nitrogenous, (b) non- nitrogenous. The chief members 

 of the first group are creatine (C 4 H 9 N 3 O 2 ) and the purin bodies hypo- 

 xanthine (C 5 H 4 N 4 O) and xanthine (C 5 H 4 N 4 O 2 ). The most important 

 non-nitrogenous extractive is sarcolactic acid (C 3 H 6 O 3 ). 



Creatine is the most abundant extractive in muscle, amounting to 

 4--45 per cent, in rabbits, -3 per cent, in oxen, -26 per cent, in frogs, 

 and -2 per cent, in hedgehogs. Chemically it is closely related to urea, 

 and can be changed into this body and a substance called sarcosine 

 by boiling with baryta water. 



Another interesting relationship of creatine is to the substance called 

 creatinine. If creatine be boiled with dilute mineral acids it loses a 



