36 PHYSIOLOGY CHAP. 



obtaining the inhibitory effect is about 8 C. For both claw 

 muscles he saw that the latent period of the inhibition produced 

 by a minimal stimulus is shorter than that which precedes con- 

 traction evoked by a similar stimulus. Lastly, he found on 

 stimulating the nerve with simple induction shocks that when the 

 tone of the muscle was very pronounced the contraction was 

 preceded by a brief depression of tone. The same was noted by 

 Gad, and later by Nagy von Kegeczy and by Cowl, for nerve- 

 muscle preparations of the frog under special conditions. 



All these researches on the reaction of striated crustacean 

 muscles to stimuli present numerous analogies with the phenomena 

 of cardiac muscle. Certain histological observations of Biedermann 

 justify the conjecture that there are two different species of nerve- 

 fibres in the crab's claw-muscles, as in the heart, some of which 

 may excite the assimilatory or anabolic processes, others dis- 

 similatory or katabolic changes. The former function like the 

 vagus fibres, the latter like the sympathetic fibres, on the heart. 

 Mangold (1905) has recently confirmed this hypothesis of a double 

 innervation of these muscles. 



VII. Alterations of form (contraction and relaxation, positive 

 and negative variations in tone) are only the external expression 

 of the physiological processes that take place within the muscle. 

 To obtain a clear idea of these, we must next investigate the 

 chemical composition of muscle, and the changes which it under- 

 goes during activity and in rest. 



Muscle undergoes a profound physico-chemical alteration after 

 death, which is termed rigor mortis. Muscles excised from the 

 body of the living animal, or merely cut off from the circulation, 

 become rigid after a certain time (varying from ten minutes to 

 several hours) i.e. they are less soft and elastic, less extensible and 

 at the same time shorter, thicker, darker, and less transparent. 

 Their alkaline or neutral reaction becomes acid. As early as 1833 

 Sommer regarded cadaveric rigidity as a coagulation phenomenon. 

 Brlicke accepted the same theory, but proof was afforded for the 

 first time in 1859 by Klihne. He showed that when the living 

 muscles of the frog were completely deprived of blood by an 

 endovascular injection of salt solution, and gradually cooled to 

 - 7 C. rubbed into fragments and squeezed under high pressure, it 

 was possible at a temperature of to separate off a fluid which 

 filtered slowly, was of syrupy consistency and slightly alkaline 

 reaction, which he termed muscle plasma. 



At the temperature of the air, muscle plasma clots as easily as 

 blood plasma, and takes on a gelatinous consistency. A fluid 

 afterwards separates out, owing to the contraction of the clot. 

 The substance that clots was termed myosin by Klihne, and the 

 liquid that separates off, muscle serum. Muscle plasma, like blood 

 plasma, begins to clot at the points of contact, and the process of 



