INVOLUNTARY MUSCULAR FIBRE. 



555 



In examining a fasciculus that had been fully stretched, 48 hours after death, 

 I met with several good specimens of isolated fibre-cells, two of which are repre- 

 sented in figs. 2 and 3. I would draw particular attention to the delicate, spi- 

 rally-twisted extremities of the fibre-cell 3, such as no tearing of a continuous 

 fibre could possibly have produced. Though these fibres are very long, yet we have 

 no reason to believe that anything near the extreme degree of extension has been 

 attained in them, and we cannot but contemplate with amazement the extent of 

 contractility possessed by this tissue. 



In fig. 16 is represented a portion of a fibre-cell curled up, which has been 

 introduced for the sake of the clear manner in which it shows the position of the 

 nucleus embedded in it. Just as in the case of the fibres wrapped round the arte- 

 ries of the frog's foot, this cell might be seen in section by proper adjustment, and 

 that section is observed to be oval ; proving that the fibre is not round, but some- 

 what flattened. It happens that the nucleus appears at this point ; its section is 

 circular, and is surrounded on all sides by the substance of the cell. 



The pig's intestine seems to be a peculiarly favourable situation for the inves- 

 tigation of unstriped muscle. Judging from Kolliker's measurements, the fibres 

 appear to be of much larger size there than in the same situation in the human 

 body. The length of the fibre-cell 3 is t V inch. The fibre 2 is imperfect at one extre- 

 mity ; but, taking the double of the distance from its pointed end to the nucleus, 

 its length is 33 inch. These measurements are between three and four times 

 greater than any which Professor Kolliker has given for the human intestine, 

 and considerably exceed the length of the " colossal fibre-cells" which he describes 

 as occurring in the gravid uterus. The individual fibre-cells, with their 

 nuclei and transverse markings, if they have any, are quite distinctly to be seen 

 with one of Smith and Beck's A object-glasses. But in order to examine their 

 structure minutely, a higher power is required : that which I use is a first-rate 

 tV, made several years ago by Mr Powell of London. All the figures in Plate XV., 

 except 17 and 18, are from camera lucida sketches, reduced to the same scale. 

 The principal measurements of the fibre-cells from the pig's intestine are as 

 under : — 



Length of fibre-cell, 3, 



Breadth of ditto, 



Length of nucleus of ditto, 



Breadth of ditto, 



Breadth of fibre-cell, 16, 



Thickness of ditto, 



Length of fibre-cell, 13, 



Breadth of ditto, 



Longitudinal measurement of nucleus of ditto 



Transverse, ditto, 



Length of fibre-cell, 15, 



~ inch. 



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