98 C. P. MARSHALL. 



Further, the action of different reagents in splitting the fibre in 

 different directions (alcohol, etc., causing longitudinal, and acids 

 transverse splitting) lends some support to the same view. Haswell* 

 in his observations on the striped muscle of the gizzard of Syllis, 

 states that after treatment 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 net- 

 work, 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 con- 

 traction is not the only function performed by muscle. The muscles, 

 as stated by Dr. Michael Foster,! 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 sources 

 of heat of the body, and are, "par excellence, the thermogenic 

 tissues." 



It thus appears that the thermogenic function of muscle absorbs a 

 far greater amount of its energy than does the contractile function, 

 and if we attribute the thermogenic function to the sarcous substance, 

 and the contractility to the network, the above objection appears to 

 receive a satisfactory answer. 



The following quotation from Dr. Michael Foster % is curiously 

 in accordance with the view of the structure and function of muscle 

 maintained above, and may fitly conclude this paper. 



" It is quite open for us to imagine that in muscle, for instance, 

 there is a framework of more stable material, giving to the muscular 

 fibre its histological features, and undergoing a comparatively slight 

 and slow metabolism, while the energy given out by muscle is sup- 

 plied at the expense of more fluctuating molecules, which fill up, so 



* " Quart. Journ. Micr Sci.," 1886. 



t "Text-book of Physiology," 4th ed., p. 461. 



I Loc. cit., p. 475. 



