204 PEACTICAL 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 S2 H 30 N 4 FeO s + 3H 2 = 2(C 16 H 18 N 2 S + Fe). 



Haematin. Haematoporphyrin. 



Solutions of haematoporphyrin exhibit a red fluorescence. This 

 pigment must be regarded as normally present in small quantities 

 in urine. 



CHAPTEE IX. 

 MUSCLE. 



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

 food-stuffs undergo combustion, as a result of which energy is liberated 

 and appears either as muscular movement or as heat. The food-stuffs, 

 along with the oxygen necessary for their combustion, are carried to 

 the muscle, and the effete products are removed by the blood going to 

 and coming from the muscle. 



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

 the form in which we take most of our proteid and a large amount of 

 our fat. 



We must accordingly study it from two standpoints, firstly as the 

 "combustion" tissue of the body, and secondly as one of the most 

 important food-stuffs. 



Chemical Composition of Muscle. 



Water, - 75 per cent. 



Proteids, 20-21 



Organic Extractives, 0'3-'4 ,, 



Fat, 2-3 



Inorganic salts, l'Q-1'3 ,, 



The Proteids. These may be divided into two classes: (1) Proteids 

 peculiar to muscle ; and (2) Proteids common to muscle and blood. 



