CHAP. IX.] THE CONTRACTILE TISSUES. 335 



The muscle of which the glycogen is to be separated, is subjected 

 to long boiling in a solution of caustic potash ; the solution is then 

 almost neutralized with hydrochloric acid, care being taken, however, 

 that the reaction still continues distinctly alkaline; solution of chloride 

 of zinc is then added to it and it is boiled for a period varying 

 between 20 and. 40 minutes ; the proteid bodies are precipitated and 

 an easily filtered clear liquid is obtained. It is of importance that 

 just enough of the zinc salt should be added to effect the precipita- 

 tion. When this point has been attained and the clear liquid is no 

 longer rendered turbid by boiling with a fresh quantity of zinc 

 chloride, it is filtered, and the precipitate carefully washed ; the filtrate 

 and washings are concentrated on a water-bath, allowed to cool, and 

 then treated with much alcohol which has been faintly acidulated 

 with hydrochloric acid. Glycogen is thus precipitated ; it is collected 

 on a filter, washed with weak spirit containing about 60 p. c. of 

 alcohol, and acidulated with hydrochloric acid, until the washings 

 contain no zinc ; the acid alcohol is then displaced by pure alcohol, 

 and lastly the substance is dried, and weighed, or heated with dilute 

 mineral acids for 2 or 3 hours, and the sugar formed determined. 



, Nasse scalds a known weight of muscle, then 



pounds it up in .a mortar with a weighed quantity 

 of quartz sand, and digests it in a beaker with water and filtered 

 saliva for some hours. He then heats the mixture to 100 C. on a 

 water bath, to precipitate soluble proteids, then weighs the beaker 

 and its contents, and determines the quantity of sugar which a 

 weighed quantity of the clear liquid contains, employing for this pur- 

 pose a Fehling's solution of which 1 c.c. corresponds to 1 milligramme 

 of dextrose. Assuming that the sugar formed from the muscle- 

 glycogen has the same reducing power as dextrose, and that it is 

 equally distributed throughout the scalded muscle and water, the 

 amount of glycogen originally present can be easily calculated. 



Proportion The amount of glycogen found in different muscles 



of glycogen of the same animal and in different individuals of the 



same species, varies so much that no general statement 



can be made. In Nasse's experiments the glycogen of 



resting muscles of frogs amounted, on an average, to 0'43 per cent. 



In rabbits the amount varied between 0'47 and 0'95 per cent. 



Abeles' results were decidedly higher. As yet, however, the total 



number of reliable determinations of the amount of glycogen in 



muscle is too small to allow of any statement being made as to the 



average amount of this constituent present. 



We shall examine in a future section the changes in the amount 

 of glycogen brought about by the passage of muscle from the state 

 of rest into that of activity or rigor. 



1 Nasse, Op. cit. p. 101 and 102. 



