THE PHYSICO-CHEMICAL BASIS OF STRIATED- 

 MUSCLE CONTRACTION (I) 



WILLIAM N. BERG 



THE ZUNTZ THEORY OF MUSCLE CONTRACTION 



In 1908 Zuntz^ advanced the following theory of muscle con- 

 traction: Muscle fibrils consist of rods or cylinders having a diam- 

 eter of i micron and a height of 6 microns. Assuming that but one 

 half of the area is taken up by rods and the other half by sarkoplasm, 

 a cross section of i c.c. of muscle would contain 62 million rods. 

 Assuming that but one half the length of the fibril is occupied by the 

 rods, there will be room, in i c.c. of muscle, for 800 layers, each 

 containing 62 million rods. Zuntz calculates that these rods have 

 an area of 8928 sq. cm. available for osmotic work. 



The beginning of the contractile process lies in the combustion 

 which takes place within the rods. The resultant carbon dioxid 

 dissolves in the water present (as if it were so much sugar) and 

 exerts an osmotic pressure of approximately 5 grams per sq. cm. 

 At the moment of their formation, the carbon dioxid molecules have 

 a temperature of over 6000° C. The osmotic pressure of the Con- 

 tents of the rods is raised, by this high temperature, to 462 grams 

 per sq. cm. 



As the result of this osmotic difference between the contents of 

 the rod and the sarkoplasm bathing it, water diffuses rapidly into the 

 rod, causing it to shorten and approach the spherical shape, i. e., the 

 muscle contracts. Presently the temperature falls through radia- 

 tion, etc.; the osmotic pressure of the carbon dioxid falls; water 

 diffuses outward, followed by a slower diffusion of the carbon 

 dioxid and other products of muscular activity; i. e., the muscle 

 relaxes. 



^ Zuntz, N. : Die Kraftleistung des Tierkörpers. Eine Festrede zur Feier 

 des Geburtstages Sr. Majestät des Kaisers. Kgl. Landw. Hochschule, Berlin. 

 1908, Pp. 34- 



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