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. 2and 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 KoLiiKer’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 ¢; 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 #; inch. These measurements are between three and four times 
greater than any which Professor Ko.tuiker 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 Sir and Becx’s xs object-glasses. But in order to examine their 
structure minutely, a higher power is required: that which I use is a first-rate - 
yz, Made several years ago by Mr Powett 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, . ; : ; ; iy auch: 
Breadth of ditto, ; ‘ y ; ‘ Tee 
Length of nucleus of ditto, : : s . - im » 
Breadth of ditto, : : . : ; ainitas: Pes 
Breadth of fibre-cell, 16, . ; ‘ ’ meget 
Thickness of ditto, é : 4 A ‘ —— 
Length of fibre-cell, 13, . é ; ; ie ‘ 
Breadth of ditto, 5 z ; y { af " 
Longitudinal measurement of nucleus of ditto, 5 : fi x 
Transverse, ditto, 5 4 : ; ae - 
Length of fibre-cell, 15, ‘ ‘ ‘ 5 cited 
