On Muscular Motion and Animal Spirits 233 



undergoes contraction, it is probable that not so much 

 the fibres, as the fibrils inserted transversely into them, 

 chiefly undergo contraction, as will be shown after- 

 wards. 



As to the swelling of the fleshy fibres observed close 

 to a ligature tied upon them, that seems to be pro- 

 duced by the blood passing through on the one side 

 and on the other, but not from the interrupted motion 

 of the animal spirits. For if such a swelled fibre be 

 wounded, blood immediately escapes in abundance. 

 Besides, that tumour remains constant at the ligature 

 even when the muscle is relaxed and is no longer 

 contracted, and then the animal spirits are not sup- 

 posed to advance out of the tendinous fibres, but, on 

 the contrary, to retire into them. 



But so far I think we may agree with the learned 

 author, for I believe that the contraction of the 

 muscles is produced by particles of different kinds 

 mixed with one another in the structure of the muscle, 

 and mutually effervescing, as will be shown below. 



I am quite aware that the learned Dr Steno, in his 

 Myologice Specimen^ published not very long ago, 

 thinks that there is no need that any elastic matter 

 should be added in order to start the contraction of 

 the muscles ; which, in this learned author's opinion, 

 can be effected by a mere change of their form. 

 Thus, '*If a muscle should change from an obHque- 

 angled parallelogram into a parallelogram the angles 

 of which are less acute, as is supposed to happen in 

 the contraction of the muscle, then it will be con- 

 tracted in length, and will also swell up, without the 

 addition of any new matter " ; as is shown in Plate III., 

 Fig. I, in which, let «, h^ c, d^ be the muscle, c, </, ^,/, 

 the same contracted, and although it be of the same 

 magnitude as before, and has had no new matter 



