PRACTICAL EXERCISES 793 



precipitation will occur in one or all of these test-tubes. To another 

 test-tube of the extract diluted in the proportion which has given the 

 best ' muscle-clot ' add a few drops of a dilute solution of potassium 

 oxalate, and place in a bath at 40. Coagulation occurs as before. 

 Filter off the clot from all the test-tubes. The filtrate is the ' muscle- 

 serum/ and yields a precipitate of serum-albumin at 70 to 73 C. 



(3) Myosinogen, like other globulins, is insoluble in distilled water, 

 but soluble in weak saline solutions. Saturation with neutral salts like 

 sodium chloride and magnesium sulphate precipitates myosinogen, but 

 not albumin, from its solutions; saturation with ammonium sulphate 

 precipitates both. Verify the following reactions of myosinogen, using 

 the original magnesium sulphate extract of the muscle : 



(a) Dropped into water, it is precipitated in flakes, which can be 

 redissolved by a weak solution of a neutral salt (say 5 per cent, mag- 

 nesium sulphate). 



(b) When a solution of myosinogen is dialyzed, it is after a time pre- 

 cipitated on the inside of the dialyzer as the salts pass out. 



(c) If a piece of rock-salt is suspended in a solution, the myosin 

 gradually gathers upon it, diffusion of the salt out through the precipi- 

 tated myosin always keeping a saturated layer around it. 



(d) Saturate a solution containing myosinogen with crystals of 

 magnesium sulphate, stirring or shaking at frequent intervals. The 

 myosinogen is precipitated. 



(e) Without adding any salt, simply shake a myosinogen solution 

 vigorously; a certain amount of the myosinogen will be precipitated 

 and the solution will become turbid. This reaction can also be ob- 

 tained with solutions of other proteins, such as albumins (Ramsden). 



Extracts qualitatively similar to those obtained from the muscles 

 of a freshly-killed animal can be got from muscles that have entered 

 into rigor, but the quantity of the various proteins going into solution 

 is less. 



1 8. Reaction of Muscle in Rest, Activity, and Rigor Mortis. (a) Take 

 a frog's muscle, cut it across, and press a piece of red litmus-paper on 

 the cut end; it is turned blue. Yellow turmeric paper is not affected. 



(b) Immerse another muscle in physiological salt solution (0-75 per 

 cent, for frog's tissues) at 40 to 42 C. It becomes rigid. The reaction 

 becomes acid to litmus-paper, and also turns brown turmeric paper 

 yellow. 



(c) Plunge another muscle into boiling physiological salt solution. 

 It becomes harder than in (b). 



(d) Stimulate another muscle with an interrupted current from an 

 induction machine (Fig. 93, p. 198), till it no longer contracts. The 

 reaction is now acid to litmus-paper. Brown turmeric paper may also 

 be turned yellow. 



(e) To demonstrate the formation of lactic acid in muscle in heat 

 rigor or fatigue, perform the following experiment: Pith a frog, and 

 afterwards leave it for half an hour at rest, so that the lactic acid pro- 

 duced in the movements connected with the pithing operation may 

 disappear from the muscles. See that the circulation in the hind-limbs 

 is not interfered with by pressure or flexion. Then remove both hind- 

 limbs. Carefully, but rapidly, remove the muscles of one from the 

 bones with as little manipulation as possible. Immediately place them 

 in a small mortar cooled in ice, and containing some sand and 20 or 

 30 c.c. of ice-cold 95 per cent, alcohol, and quickly grind them up. 

 Produce heat rigor (p. 751) of the muscles of the other hind-limb, or 

 fatigue them with induction-shocks, and then grind them up under 

 alcohol in the same way. Filter the alcoholic extracts, and then 



