626 A MANUAL OF PHYSIOLOGY 



of electrodes. Its value in time is given by the tracing of the tuning- 

 fork. The length of the nerve between the two pairs of electrodes 

 is now carefully measured with a scale divided in millimetres, and the 

 velocity calculated (p. 603). 



21. Chemistry of Muscle. Mirice up some muscle from the hind- 

 legs of a dog or rabbit (used in some of the other experiments), of 

 which the bloodvessels have been washed out by injecting normal 

 saline solution through a cannula tied into the abdominal aorta until 

 the washings are no longer tinged with blood. To some of the 

 minced muscle add twenty times its bulk of distilled water, to another 

 portion ten times its bulk of a 5 per cent, solution of magnesium 

 sulphate. Let stand, with frequent stirring, for twenty-four hours. 

 Then strain through several folds of linen, press out the residue, and 

 filter through paper, (i) With the filtrate of the watery extract make 

 the following observations : 



(a) Reaction. To litmus paper acid. 



(b) Determine the temperatures, at which coagulation of the various 

 proteids in the extract takes place, according to the method described 

 on p. 2i.* Put some of the watery extract in the test-tube, and 

 heat the bath, stirring the water in the beakers occasionally with a 

 feather. Note at what temperature a coagulum first forms. It will 

 be about 47 C. Filter this off, and again heat ; another coagulum 

 will form at 56 to 58. Filter, and heat the filtrate ; a third slight 

 coagulum may be formed at 60 to 65 C. A fourth precipitate 

 (of serum-albumin) will come down at 70 to 73. Saturate some 

 of the watery extract with magnesium sulphate ; a large pre- 

 cipitate will be formed, showing the presence of a considerable 

 amount of globulin. Filter off the precipitate and heat the filtrate ; 

 coagulation will again occur at very much the same temperatures as 

 before, although the total amount of precipitate will be less. Note in 

 particular that there is still some precipitate at 47 to 50. Para- 

 myosinogen possesses some of the characters of both globulins and 

 albumins, for it is partially but not entirely precipitated by saturation 

 with magnesium sulphate, and is not precipitated by sodium chloride. 



(2) (a) Test the reaction of the magnesium sulphate extract. It 

 will usually be faintly acid to litmus. 



(b) Heat some of it. Precipitates will be obtained at the same 

 temperatures as in (i) (b\ but those at 47 to 50 and 56 to 58 will 

 be more abundant. Of the two, that at 47 to 50 will usually be the 

 larger when time is given for it to come down and the heating is 

 gradual. 



(c) Dilute some of the magnesium sulphate extract with three 



* It should be remembered that the temperature of heat-coagulation of 

 any substance is by no means an absolute constant. It depends on the 

 reaction, the proportion and kind of neutral salts present, perhaps on the 

 strength of the proteid solution and the manner of heating. A solution 

 of egg-albumin, e.g., can be coagulated at a temperature much below 70 

 when it is heated for a week. Small differences in the temperature of 

 heat-coagulation, unless supported by well-marked chemical reactions, 

 are not enough to characterize proteid substances as chemical individuals. 



