322 PRACTICAL PHYSIOLOGY 



Hypoxanthine and xanthine result in part from the breakdown of 

 the nuclein present in the muscle, but their amount is normally so large 

 compared to the amount of nuclein present that this cannot be their 

 sole source ; the other source of supply is at present unknown. 



Lactic Acid (C 3 H 6 O 3 ). This variety of lactic acid differs from that 

 obtained by the fermentation of lactose, which does not rotate the plane 

 of polarised light. The lactic acid of muscle, often termed sarcolactic 

 acid, rotates the plane of polarised light to the right. The amount of 

 lactic acid increases markedly during the death of a muscle, and also 

 during muscular activity. These points can be shown by the following 

 experiments : 



(a) To some of Uffelmann's reagent (a mixture of ferric chloride and 

 carbolic acid) add some of the muscle extract provided. This probably 

 contains lactic acid from the dying muscle ; if it does the violet colour 

 of Uffelmann's reagent will be turned to yellow by the lactic acid present. 



(6) Hopkins' Test for Lactic Acid. Take about 5 c.c. of strong 

 sulphuric acid in a dry test tube, add 1 or 2 drops of a solution of muscle 

 extract, 2 or 3 drops of saturated solution of copper sulphate. Warm 

 in boiling water for about two minutes ; cool and add a few drops of 

 alcoholic thiophene solution (20 minims in 100 c.c. alcohol), and warm 

 gently. With lactic acid a cherry red colour develops. 



(c) Take a pithed frog which has been kept on ice for half an hour. 

 Quickly cut off the muscles of one hind limb ; cut off the other limb at 

 the pelvic girdle, and stimulate electrically until irritability is nearly 

 lost. Cut off the muscles. Treat both sets of muscles as follows : 

 Grind with cold absolute alcohol and sand, filter, evaporate the alcohol, 

 dissolve in water, heat with a little animal charcoal, filter, evaporate, and 

 apply the thiophene test. It will be found that the muscles of the 

 tetanised limb give a positive reaction ; those of the non-tetanised do 

 not. 



Another important nitrogen-free extractive is glycogen (C 6 H 10 O 5 )n. 

 The relative amount of this is small (0-5 to Iper cent.,), but it varies in 

 different animals, and is much diminished after muscular activity. 



Other extractives are : Urea, carnosine, dextrose (trace), inositol 

 (hexahydroxybenzene), and lecithin. 



Inorganic Salts. -These consist of salts of the alkalis and alkaline 

 earths. The chief acid radicle present is phosphoric acid, and this 

 exists in several states (a) Inorganic phosphates, (b) phosphorus of 

 lecithin, (c) phosphorus of nuclein, (d) phosphorus of other organic 

 compounds. 



EXPERIMENT VI. The watery extract of muscle has been freed of 

 proteins by boiling it. Add to the clear filtrate an ammoniacal solution 

 of magnesium citrate. A white precipitate of phosphates results. 

 Show that this precipitate consists of phosphates by dissolving it in 

 nitric acid and testing with ammonium molybdate. 



Preparation of Extractives of Muscle. 500 gms. of meat, from 

 which as much fat and tendon as possible have been removed, are finely 

 minced ; the mince is thoroughly mixed with 500 c.c. of water and 

 heated for half an hour on a waterbath at 50 C. The extract is 

 strained through muslin and the residue extracted several times in a 

 similar manner, the extracts being mixed together. The protein in the 

 extract is then coagulated by boiling, and, after cooling, the coagulum 

 removed by filtration. 





