CHEMICAL PHENOMENA OF MUSCULAR CONTRACTION 749 



serum-albumin belongs to the blood and lymph, and is not a constituent 

 of the muscle-fibre. The most recent work on the subject is that of 

 Botazzi, who obtained muscle juice without the addition of water or 

 salt solutions, by rubbing muscles up with sand, and then subjecting the 

 triturated material to a pressure of many atmospheres. He finds that, 

 leaving out of account the serum-albumin, muscle juice contains only 

 one protein in solution, and this corresponds upon the whole in its 

 properties to myosinogen. A second protein, and only these two have 

 been proved to exist in muscle juice, is not in solution, but in the form 

 of very fine granules revealed by the ultramicroscope. This corresponds 

 in a general way to paramyosinogen. Botazzi supposes that it repre- 

 sents the substance of the muscular fibrils. The granules show a ten- 

 dency even at the ordinary temperature to agglutinate and to be pre- 

 cipitated. The process is hastened by dilution with water, removal of 

 the salts by dialysis, addition of acids, and the agglutination and pre- 

 cipitation are accomplished very rapidly at 45 to 55 C., giving rise 

 to ' heat coagulation.' The protein in solution (myosinogen) is in- 

 soluble in distilled water when thoroughly freed from salts, and is pre- 

 cipitated by dialysis, but not so easily as paramyosinogen. The total 

 proteins in the juice obtained by pressure varied from 5*3 to 9-5 per 

 cent., a great deal of the muscle protein being, of course, left in the 

 residue. The granules (paramyosinogen) constituted from a third to 

 two-thirds of the protein in different experiments, and the true pro- 

 portion must have been considerably higher, since on account of their 

 small size the loss in separating them by filtration was great. The 

 ' myosin ' precipitate, which rapidly forms in muscle-plasma at body 

 temperature, is sometimes called the muscle-clot, and the liquid which 

 is left the muscle-serum, but it would probably be better to avoid these 

 terms, as they suggest an analogy with the coagulation of blood-plasma, 

 which is apt to be misleading. A similar precipitate or clot seems to 

 be formed in the interior of the muscular fibres in natural rigor and in 

 the rapid rigor produced by heating a muscle to a little above the body- 

 temperature. But in natural rigor the whole of the paramyosinogen 

 and myosinogen do not undergo the change, since a certain amount of 

 these substances can as a rule be extracted from dead muscle by saline 

 solutions. Thus, in rabbit's muscles, before the onset of rigor mortis, 

 873 per cent, of the total protein was found to be soluble in 10 per cent, 

 ammonium choride solution, and only 12-7 per cent, coagulated; while 

 after rigor had occurred, 71*5 per cent, was coagulated, and only 28-5 per 

 cent, remained soluble (Saxl). It is not known whether in the living 

 muscle paramyosinogen and myosinogen exist as such. It has, indeed, 

 been stated that, if a tracing is taken from a muscle which is gradually 

 heated, it first shortens at the temperature of coagulation of para- 

 myosinogen, and then again at that of myosinogen, and that in frog's 

 muscle there is an additional shortening at 40, the temperature at 

 which in extracts an additional heat precipitate occurs. The conclusion 

 has been drawn that these substances must be present as such in the 

 living fibres, and that the successive shortenings are mechanical phe- 

 nomena due to their heat coagulation. Similar shortenings have been 

 described in nerve'and liver tissue at about the temperatures at which 

 the proteins in extracts of these tissues are coagulated by heat. But 

 Meigs has shown that the supposed correspondence is far from being 

 exact, and that muscles whose proteins have been already coagulated in 

 a mixture of alcohol and salt solution still show the typical shortening 

 on being heated. The heat shortening is, therefore, dependent on 

 some other process than aggregation of the particles of coagulable 

 protein. 



