350 PRACTICAL PHYSIOLOGY 



acid solution, show two bands, the centres being approximately A. 605 

 and A. 565 (Spectrum 10 in Chart). 



If a large excess of water is added to the above a precipitate is 

 thrown down. If this be dissolved in a little caustic soda, a solution 

 of haematoporphyrin in an alkaline medium is obtained, which shows 

 a four-banded spectrum when examined, the positions of the bands 

 being A 630, A. 580, A, 550, and A. 520 approximately (Spectrum 11 

 in Chart). 



Haematoporphyrin may be regarded as iron-free haematin, and 

 identical in composition with bilirubin. The following equation 

 represents the change brought about by sulphuric acid : 

 C 32 H 30 N 4 Fe03 + 3H 2 = 2(C 16 H 18 N 2 3 + Fe). 



Haematin. Haematoporphyrin. 



Solutions of haematoporphyrin exhibit a red fluorescence. This 

 pigment must be regarded as normally present in small quantities 

 in urine. 



CHAPTER X. 

 MUSCLE. 



MUSCLE forms the most abundant tissue in the body. It is here 

 that a great part of the food- stuffs undergo combustion, as a result of 

 which energy is liberated and appears either as a muscular movement 

 or as heat. The food-stuffs, along with the oxygen necessary for their 

 combustion, are carried by the blood to the muscle, and the effete 

 products are removed by the blood coming from the muscle. 



Muscle also constitutes one of the commonest food-stuffs, meat being 

 the form in which we take much of our protein and a considerable 

 amount of our fat (see chapter on Food). 



The Chemical Composition of Muscle. 



Water, - 75 per cent. 



Proteins, 20-21 



Organic Extractives, 0'3-'4 ,, 



Fat, 2-3 



Inorganic Salts, 1-0-1 3 



The Proteins. To study these we require a muscle extract. 



Preparation of Muscle Extract. 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 



