Licence: Public Domain Mark
Credit: Cilia / by W. Sharpey. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![ternal gills exhibited tlie same phenomena, but he could discover nothing of the kind on the internal gills. ^ Gruithuisen* observed in the tadpole of the Gre.en Frog that so soon as the circulation of the blood began in any part of the gills, small ob- jects were attracted and repelled from that spot, and that the same took place a few days later on the tail wherever vessels had been farmed. He conceived that the motion of the water was for the purpose of exposing the blood to its in- fluence, and compared it to the current pro- duced by Infusoria by means of cilia. He does not say, however, that he had seen cilia in the tadpole. Huschkef observed that the water in the vicinity of the gills of the young Salamander was thrown into a boiling-like motion, while it flowed steadily at other parts of the body. Without being aware of these previous disco- veries, I was led in 1830, by an accidental ob- servation of my own, to go over nearly the same ground.]; I had cut off one of the external gdls of the tadpole of the Frog, and placed it with a drop of water under the microscope, with the view of measuring the size of the glo- bules of blood that might flow from it, and was astonished to perceive that the globules, on escaping from the cut part of the gill, moved rapidly along its surface towards the points of the branches in a constant and uniform manner. On further inspection it soon became evident that the blood-globules were entirely passive in their motion, and that other light particles brought near the gills were moved in a similar manner; their motion being manifestly owing to a current produced in the water along the surface of the gill in a determinate direction. ■A conclusive proof of this was afforded by put- ting the gill which had been cut off, into a watch-glass with a larger quantity of water. It was then seen that when the gill happened to be fixed by any obstacle, small bodies in its vicinity were moved along it as before towards the points of the branches, but when unim- peded the gill itself advanced through the water in a direction contrary to that in which the particles were moved, the trunk being turned forward; the tendency to produce a current in one direction, thus causing the gill, now no longer fixed, to move in the opposite one. The current began at the root of the gill, and ran along the branches, at the points of which it did not continue its primitive direc- tion, but turned off sideways, and immediately ceased. (See Jig. 21, C). I soon found that the gill was not the only part of the animal which excited motion in the water. Nearly the whole surface of the body produced the same effect. A general current commenced on the fore part of the head, pro- ceeded along the back and belly and the two * Salzburg. Medicinisch-Chirurgische Zcitung, 1819, ii. p. 447. f Isis, 1826, p. 625, (cited in Burdach's Physio- logic, from which I quote, not having seen the ori- ginal.) \ Edinb. Med. and Surg. Journal, xxxiv. sides, to the tail, along which it continued to its extremity. It was not so strong as that on the gills, but agreed with it in other respects. I continued for some time to observe the phenomenon in the larva of the Frog, in order to find out whether it underwent any alteration in the progress of the developement of that animal. It is known that after a time the ex- ternal gills become covered by a fold of the skin, and inclosed in the same cavity with the internal gills, when they gradually shrink and at last disappear. On examining the animal while this change was taking place, and for some time after, it appeared that the external gills after their inclosure still retained their peculiar property, and continued to do so as long as any portion of them remained; the current on the body remained the same; on the tail it acquired a twofold direction diverging from the middle part or continuation of the vertebral column, obliquelyupwards and down- wards towards the upper and lower edge. As the animal advanced in growth, the currents gradually disappeared over the greater part of the surface, continuing longest at the posterior part of the body; at length, when the pos- terior extremities were so far advanced in growth that the thigh, leg, and toes could be discerned with a magnifying glass, which was the latest period of observation, the current existed only at the commencement of the tail, and on a small part of the body near the hind leg. The internal gills, though tried in various stages of development, did not exhibit the phenomenon. I next sought for the same appearances in the larva of the Newt or Water Salamander, which was first examined a few days after its exclusion from the egg when its gills are ^*»ry simple. At this period the surface of the animal produces currents agreeing in almost every circumstance with those which take place in the larva of the frog at a correspond- ing stage of its development. Particles of powder diffused in the water are carried along the surface of the body from before back- wards; on the gills they are conveyed along each of the trunks from the root to the ex- tremity. The gills also, when cut off, move through the water with the cut extremity for- wards, in a direction contrary to the currents. I have since found nearly the same phenomena in the gills at a much later period. It was evident that the purpose of these currents was to effect a renewal of the water on the respiratory surfaces; respiration in these animals probably being performed not only by means of the gills, but also by the general sur- face of the body. It appeared that the power of impelling the water was wholly confined to the external sur- face of the animal; a portion of the skin being raised and detached, floating bodies were moved along its external surface only. Parts cut off from the animal continued to excite currents for several hours after their separation, and the smallest portion produced that effect. In these cases the current always moved in the same direction relatively to the surface of](https://iiif.wellcomecollection.org/image/b22282580_0028.jp2/full/800%2C/0/default.jpg)
