OBSERVATIONS ON STRIPED AND UNSTRIPED MUSCLE. 103 



transverse bars of the same network. This is an objection, 

 the real nature of which it is impossible to determine in the 

 present state of our knowledge of the nature and import of 

 intracellular networks in general. In unstriped muscle the 

 longitudinal fibrils are alone present, and in the development of 

 striped muscle the longitudinal elements of the network appear 

 first. The transverse networks are described and figured by 

 Retzius as direct processes of the muscle-corpuscles; the mode 

 of their development is as yet unknown, but should they prove 

 on further investigation to develop as processes of the 

 corpuscles, it would follow that the two elements of the 

 network are, in spite of their close connection in the adult, of 

 entirely independent and different origin. And then a differ- 

 ence of function would become not only possible but highly 

 probable. Further, the action of different reagents in split- 

 ting the fibre in different directions (alcohol, &c, causing 

 longitudinal, and acids transverse splitting) lends some 

 support to the same view. Haswell 1 in his observations on the 

 striped muscle of the gizzard of Syllis, states that after treat- 

 ment with hsematoxylin, and then glacial acetic acid, the 

 transverse networks are stained, but not the longitudinal ; he 

 says this may point to some difference in the substance of 

 which they are composed. 



2. This theory attributes the function of contraction to the 

 network which forms much less of the bulk of the fibre than 

 does the sarcous substance, the latter being far greater in 

 amount than the network. In reference to this it should be 

 borne in mind that contraction is not the only function per- 

 formed by muscle. The muscles, as stated by Dr. Michael 

 Foster, 3 are continually undergoing metabolism, giving rise to 

 a certain amount of heat; the metabolism during rest being 

 slow, but suddenly increasing during contraction. The energy 

 involved in the work done in a muscular contraction is only 

 about one tenth the total energy expended, the rest going out 

 as heat. Hence the muscles must be regarded as the chief 



1 ' Quart. Journ. Micr. Sci.,' 1886. 



2 ' Text-book of Physiology,' 4th ed., p. 461. 



