ELEMENTARY PHYSIOLOGICAL CHEMISTRY 205 



EXPERIMENT I. A rabbit is killed, and a cannula tied into 

 its aorta, by which the blood-vessels are washed free of blood. 

 The muscles are then removed and quickly passed through the 

 mincing machine. The mince is then mixed with a 5 per cent, solution 

 of magnesium sulphate, the mixture being placed on ice and left 

 standing all night. The resulting extract, strained through muslin,, 

 should be prepared beforehand by the demonstrator. 



Divide it into two parts, a and b. 



(a) Dilute with four volumes of water, and place in the water-bath at 

 body temperature. A clot forms. 



(b) Add some acetic acid. A precipitate forms. Filter. Neutralise 

 the nitrate with Na 2 C0 3 solution, and dilute it with water. Place it in 

 the water-bath, and note that no coagulum forms. 



These two experiments show us that the extract contains in solution 

 a substance which is precipitated by acetic acid, and which becomes 

 transformed into an insoluble clot under suitable conditions. This body 

 is proteid in nature, as can be proved by dissolving the clot in (a) a 

 10 per cent, sodium chloride and applying the proteid tests. The 

 soluble body is called myosinogen, and the clot myosin. 



Besides myosinogen the extract contains, however, other proteids. 



EXPERIMENT II. Take some of the muscle serum in (a), or of the 

 nitrate in (b), and half saturate with ammonium sulphate. A precipitate 

 of globulin results. Filter off this globulin and test the nitrate for 

 albumin. 



Organic Extractives. (For preparation of extract see Advanced 

 Course, p. 439.) These are organic substances, which are soluble in 

 water, and which are not proteid in nature. 



These are divided into two classes : (a) Nitrogenous and (/3) Non- 

 Nitrogenous. 



(a) The former group include creatin and alloxuric bodies ; creatine 

 (C 4 H 9 N 3 2 ) is the most abundant extractive in muscle 1 (0-2-0*3 per 

 cent.). Chemically it is very closely related to urea, and can be changed 

 into this by boiling with baryta water (see Advanced Course, p. 440). 

 By boiling with dilute mineral acids it loses a molecule of water, and 

 changes into creatinine, in which form it appears in the urine. The 

 total amount of creatine in the muscles is over seventy grammes, but the 

 amount of creatinine in the urine per diem is only about one gramme. 

 On the other hand, the urine contains about thirty grammes of urea 

 per diem, whereas the muscles contain only a trace. These facts, taken 

 in conjunction with the close chemical relationship, of creatine to urea, 



*It crystallises out from the proteid-free muscle extract after this has been 

 evaporated to a syrup (see Fig. 147). 



