172 CONCLUSION ON 



only after many considerations, such as are given 

 above, that the strength of these arguments is 

 weakened, and the power of a substance so constituted 

 physically to exert such force is discredited.* On the 

 other hand, examples are wanting of a dead substance- 

 physically so constituted as the muscular fibre, con- 

 tracting so powerfully under any known force. The 

 analogy of the galvano-magnetic machine is only a 

 very remote one, for the soft iron is from its nature 

 already capable of becoming a magnet in other ways. 

 In short, we are wholly ignorant of the intimate me- 

 chanism of the act of contraction, and cannot tell from 

 that whether it be a vital or a physical act ; for the 



* As before said, tlie question of tlie dependence of muscular con- 

 traction on vital protoplasmic movements of the fibre itself, must be 

 looked on rather as one not yet raised than as settled, and most physi- 

 ologists seem to take it for granted. For instance, Dr. B. Sanderson at 

 once concludes that the contraction of the leaf of the Dionsea muscipula 

 is of the same nature as that of the muscles of vertebrates. He says 

 also, that in muscular contraction an exactly similar change of shape- 

 in every particle of the muscle takes place ; for " a muscle is not an 

 apparatus made up of parts differing from each other in structure, but 

 a mass of substance equally instinct with life in every part." Also, that 

 in the plant the agent of contraction is the protoplasm of the cells of 

 the contractile organs, which, under stimuli, undergoes a most peculiar 

 change of form and arrangement. With all respect due to so high an 

 authority, I cannot accept the inference that because the contraction of 

 the plant leaf depends on changes, apparently in the contents of the 

 cells, the muscular contraction of the higher animals is of the same 

 nature. By a parity of reasoning we should be compelled to conclude 

 that the functions of respiration and digestion are not performed by 

 the special apparatus provided for them in the higher animals, because 

 these functions can be performed, in a kind of a way, by formless masses 

 of sarcode. The causes of the movements and the locomotion of the 

 Diatoms, Desmids, Bacteria, and flagelate Infusoria, and also the ciliary 

 motions, are as yet unknown, though it may be allowed they are in 

 some way dependent on the existence of protoplasm. And although a 

 mechanism through which it can work in these organisms is not yet 

 distinctly known, that forms no reason why a physical mechanism 

 should not exist in the muscular fibre, nor that the latter should be 

 *' instinct with life in every pai-t." 



