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D. E. PHILPOTT, A. SZENT-GYORGYI 



VOL. 12 (1953) 



with relatively little force. Consequently, at rest-length the muscle has a definite, though 

 relatively low, elastic tension. Fig. 2 shows the muscle in this condition. The dark line 

 in the middle is a Z membrane. The short dark lines in the left top corner and the right 

 bottom corner are also Z membranes. The figure shows the M membrane and the closely 

 adjoining H-bands unchanged. At the site of the latter (H-band) a new segment of 



l''ig. 2. I'lxplanalion in text. 



relatively low density has appeared. Evidcntlx' part of tlu' material adjoining the H-band 

 has to some extent been stretched, and the stretching has decrea.sed its density. This 

 new band of low density we will call the "Ivband"'. The width of tlie two E-bands 

 corresponds to about io°o of the whole height of one sarconier. Tlu' apjx^irance of this 

 band thus accounts for half of the gain in length from ecpiilibrium to rest-length. 

 The resting muscle can be stretched reversibly from its rest-length by about 45%. 

 Fig. 3 shows a muscle stretched by 40",, from its rest-length. If we call rest-length 



References p. 133. 



