CHEMICAL CHANGES IN MUSCLE 21fi 



THE PRODUCTION OF LACTIC ACID IN SURVIVING MUSCLE 

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

 acid formed m the fermentation or souring of milk. They both have t), 

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

 into alcohol cooled to C. While in this ice-cold alcohol they were finely divided 

 with scissors and then pounded up in a cooled mortar. In this way the tissue was 

 destroyed at a temperature which did not allow of the changes responsible in sur- 

 viving muscle for 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 pro- 

 duced 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. 

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

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

 which serves to catalyse the oxidation that follows. To this mixture a few drops ot 

 the 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 

 cooled the moment after its appearance. 



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

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

 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 temperature 

 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 

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

 acid. 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 

 kept warm. It is interesting to note that the amount of lactic acid four 

 in rigid muscle is almost invariable whatever the previous history of 1 

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

 cold alcohol, it is found to contain about -2 per cent, lactic acid. 

 ever, it be allowed to stand after mincing, there is a slow producl 

 lactic acid up to the maximum 4 per cent. Again, a muscle whi larbee 

 tetanised to exhaustion contains about -2 per cent, lacti 

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



