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CHEMICAL CHANGES IN MUSCLE 215 



THE PRODUCTION OF LACTIC ACID IN SURVIVING MUSCLE 



The lactic acid formed in muscle (sarcolactic acid) is a physical isomer of the lactic 

 acid formed in the fermentation or souring of milk. They both have the formula 

 CH 3 .CH(OH).COOH, i.e. they are ethylidene lactic acids. The lactic acid of fermenta- 

 tion is optically inactive ; sarcolactic acid rotates polarised light to the right ; while 

 a third isomer which is Isevo -rotatory is produced by the action of various bacilli and 

 vibriones on cane sugar. The sarcolactic acid can be extracted from the muscle by 

 means of alcohol. 



It was pointed out by Hopkins and Fletcher that most of the methods previously 

 used for the extraction of lactic acid from muscle caused the formation of lactic acid 

 in this tissue. To obviate this difficulty, they adopted the precaution of cooling 



muscles before cutting them out of the body and then dropping them into alcohol 



ed to 0C. While in this ice-cold alcohol they were finely divided with scissors 

 d then pounded up in a cooled mortar. In this way the tissue was destroyed at 

 temperature which did n9t allow of the changes responsible in surviving muscle 



the production of lactic acid. It is generally separated in the form of the zinc 

 sarcolactate, by boiling its partially purified solution with zinc carbonate. Its presence 

 may be tested for by means of Uffelmann's reagent, which is made by the addition of 

 ferric chloride to dilute carbolic acid. The purple solution thus produced is at once 

 changed to yellow by the addition of even traces of lactic acid. 



A much more definite colour reaction for lactic acid has been introduced by Hopkins, 

 test is carried out in the following way. About 5 c.c. of. strong sulphuric acid 



placed in a test-tube together with one drop of saturated solution of copper sulphate, 

 hich serves to catalyse the oxidation that follows. To this mixture a few drops of 

 e solution to be tested are added, and the whole well shaken. The test-tube is now 

 placed in a beaker of boiling water for one or two minutes. The tube is then cooled 

 under a water-tap, and two or three drops of a very dilute alcoholic solution of thiophene 

 (ten to twenty drops in 100 c.c.) are added from a pipette. The tube is replaced in 

 the boiling water and the contents immediately observed. If lactic acid is present the 

 fluid rapidly assumes a bright cherry red colour, which is only permanent if the tube be 

 led the moment after its appearance. 



A study of the lactic acid content of muscle by Fletcher and Hopkins, 

 ng the precautions described above, has shown that fresh muscle contains 

 nly minimal amounts of lactic acid, the quantity being smaller, the greater 

 the care that is taken to avoid injury to the muscle and to keep its tempera- 

 ture low until sufficient time has elapsed for its vital chemical processes to be 

 destroyed by the action of the cold alcohol. If the muscle be left in the 

 body after the death of the animal or be excised, a steady formation of 

 lactic acid takes place, which is more rapid in the first few hours after 

 death, but continues until the muscle passes into rigor. With the complete 

 nset of rigor, frog's muscles are found to contain about 4 per cent, lactic 

 id. After this time the amount does not increase. The onset of rigor 

 and the rate of production of lactic acid are quickened if the muscle be 

 ke,pt warm. It is interesting to note that the amount of lactic acid found 

 in rigid muscle is almost invariable whatever the previous history of the 

 muscle. Thus, if the muscle be finely minced and then extracted with 

 Id alcohol, it is found to contain about -2 per cent, lactic acid. If how- 

 er it be allowed to stand after mincing, there is a slow production of 

 actic acid up to the maximum 4 per cent. Again, a muscle which has been 

 tetanised to exhaustion contains about -2 per cent, lactic acid. When 

 allowed to undergo rigor, the amount rises to about 4 per cent. 



