340 PHYSIOLOGICAL CHEMISTRY 



an accurate separation by this method is somewhat doubtful. It is 

 well established that para-myosinogen is a globulin since it responds to 

 certain of the protein precipitation tests and is insoluble in water. 

 Myosinogen, on the contrary, is not a typical globulin since it is 

 soluble in water. It has been called a pseudo-globulin. Myosin pos- 

 sesses the globulin characteristics. It is insoluble in water but soluble 

 in the other protein solvents and is precipitated from its solution upon 

 saturation with sodium chloride. 



Mellanby has reported observations which he claims indicate that 

 there is only one protein in muscle and that rigor mortis is due to the 

 coagulation of this protein under the combined influences of the salt 

 present in the muscle and the lactic acid developed upon the death of 

 the muscle. He further states that the disappearance of rigor is due 

 to the fact that the lactic acid which is continually formed brings this 

 protein into solution. There is a difference of opinion as to whether 

 true rigor ever occurs in connection with non-striated (smooth) 1 

 muscle. 



Our ideas concerning the cause of rigor have undergone an im- 

 portant revision in recent years. A very attractive theory has been 

 advanced by Meigs 2 and experimental confirmation has been accorded 

 it by von Fiirth and Lenk. 3 According to this theory, rigor has no 

 connection with the coagulation of the muscle proteins and may even 

 be hindered or prevented by such coagulation. The cause of rigor, 

 from this new viewpoint, lies in the imbibition of water by the muscle 

 colloids. It is well known that colloids possess the property of absorb- 

 ing whatever fluid may be in contact with them. Moreover, the 

 capacity of the colloid for water is increased if the fluid is slightly acid 

 in reaction. Therefore the postmortem production of lactic acid 

 facilitates the imbibition of muscle fluid by the muscle colloids. 

 Under such conditions, the fibers swell, become rigid and the condition 

 known as rigor mortis results. The disappearance of rigor is believed 

 to be due to the coagulation of the muscle protein through the agency 

 of the accumulated lactic acid. This change is accompanied by a re- 

 lease of the imbibed water by the colloids, inasmuch as the capacity 

 of a colloid for retaining fluid is lowered by coagulation. 



Under the name extractives we class a number of muscle constituents 

 which occur in traces in the tissue and may be extracted by water, 

 alcohol, or ether. There are two classes of these extractives, the non- 

 nitrogenous extractives and the nitrogenous extractives. Grouped under 



1 Saxl: Beitrage zur chemischen Physiologie und Pathologie, 9, i, 1907. 



2 Meigs: American Journal of Physiology, 26, 191, 1910. 



3 von Fiirth and Lenk: Wiener klinische Wochenschrift, 24, 1079, 1911. 



