OBSERVATIONS ON STRIPED AND UNSTRIPED MUSCLE. 91 



On careful examination of the network in one of these fixed waves 

 of contraction with the ^ immersion objective, the longitudinal 

 fibrils of the network were always straight in all parts of the fibre, and 

 appeared slightly thicker in the contracted part of the fibre, although it 

 was difficult to judge accurately of the difference in thickness. The 

 nodal dots, however, were the same size in loth the contracted and relaxed 

 portions of the fibre. The dots appeared in many cases even smaller 

 in the contracted than in the relaxed muscle. This is, I believe, due 

 to their being more separated from each other laterally, whereby the 

 refractive effects which somewhat obscure the real size of the dots in 

 the relaxed muscle are diminished (Fig. 14). 



It therefore appears from gold preparations that during contraction 

 the nodal dots do not alter in size, but that the longitudinal bars 

 of the network increase in thickness. The apparent enlargement of 

 the nodal dots when the fibre is seen in the fresh state is due to 

 optical effect. Moreover, if the nodal dots do not alter in size, it 

 follows necessarily that the longitudinal bars must increase in 

 thickness ; for since they keep straight during contraction, if they 

 do not increase in thickness there must be a diminution in the 

 volume of the fibre, which is known not to occur. 



These results differ from the account given by Schafer of the 

 changes during contraction. He states* from observations on the 

 living fibre that during contraction his " muscle-rods " (which corre- 

 spond to the longitudinal bars of the network) become compressed 

 in the centre, and their substance tends to accumulate towards the 

 ends, i.e., that the knobbed ends of the muscle-rods, which correspond 

 to the nodal points of the network, increase in size at the expense of 

 the shafts connecting them. On examination of the living fibre this 

 certainly appears to be the case, but the optical effects of reflection 

 and refraction are so great as to obscure the real change that takes 

 place. 



Nature and Function of the Network. 



In discussing the theory of contraction, I shall assume that the 

 intracellular network of striped muscle and the longitudinal fibrils of 

 the vertebrate unstriped muscle, are of the same nature as other 

 intracellular networks; and, in accordance with the views of modern 



* "On the Leg-muscles of the Water-beetle," "Phil. Trans.," 1873. 



