The Zoologist/4th series, vol 5 (1901)/Issue 722/Sloughing in Serpents, Leighton
SLOUGHING IN SERPENTS.
By Gerald Leighton, M.D.
The process, common to all reptiles, of periodically casting off a "slough" is a very interesting one to watch, and can best be observed in serpents. It is not often the good fortune of the observer to be able to see it in natural conditions, though I have encountered several Adders engaged in the act; but in serpents in captivity the whole process can be studied with ease and accuracy. In books which touch on the subject three statements are to be found, which, in my experience, are inaccurate, or at any rate only partially true. It is said, in the first place, that the slough is cast once every year; secondly, that the reptile often makes a meal of the cast-off slough; and, thirdly, that the slough is cast entire (i.e. in one piece) when the reptile is in good health, but in several pieces if the animal is out of condition. It is quite possible that various species exhibit individual peculiarities in this matter, but in the case of British reptiles none of these statements are quite accurate. In the first place, it is usual for both Adders and Ring-Snakes to cast their sloughs three, four, or even five times in a season. The first sloughing takes place immediately after the winter hibernation is over, and the process is repeated at intervals of six weeks or two months. The same remark applies to the Slowworm (Anguis fragilis). Secondly, I doubt whether any one of the three species mentioned ever swallows the cast-off slough—at any rate, those I have kept have never done so. It is no doubt true that some amphibians do this, and probably this accounts for the idea that serpents act in a similar manner. The third point is perhaps the most interesting, and it is that to which I wish specially to draw attention in this paper. What determines whether the slough comes off whole or in pieces? To answer this question it is necessary to understand the nature of the process. There are two distinct stages in the act of sloughing. The first is an active physiological process on the part of the serpent, as the result of which the external covering is separated from the true skin. Prof. Packard describes this separation as being due to the growth of fine temporary cuticular hairs. Thus loosened, the slough rapidly becomes dry, and is ready to be cast off. The second stage, or the casting off, is a mechanical process, by which the serpent endeavours to rid itself of what is now no longer a part of its anatomy. This is effected by continuous rubbing against any convenient surface, the side of the cage in the case of captive snakes. The result of this rubbing, as far as the slough is concerned, depends, in my opinion, on the simple factor of whether the serpent is in a position to rub off both sides of the slough evenly—that is to say, if the reptile can get pressure evenly exerted on both sides of the body—by creeping through grass, or in some other way—the slough will peel off whole, being turned inside out in the process; but if, on the other hand, any projecting point should come in contact with one side of the slough, the latter, being very delicate, will be torn, and the slough cast in pieces. In very young, and therefore small snakes, the slough comes off very readily, and generally entire; but in older and larger specimens I have found it the exception rather than the rule for this to occur, and the slough is usually in pieces. This is quite independent of the state of health of the snake, a matter which is, moreover, somewhat difficult of diagnosis, unless the reptile is suffering from canker. I have made a point of observing this sloughing in reptiles in various zoological collections, and invariably have seen the sloughs of the larger serpents in pieces in the cages. Anyone can observe it at the Zoo. It is particularly noticeable in the Pythons; and I now append a series of notes made by Mr. W.J. Clarke, of Scarborough, on the frequency and character of the sloughings of one of his Pythons:—
Python molurus.—Sloughing in confinement (W.J. Clarke, Scarborough).
"I received the Python on Sept. 7th, 1897. Three weeks later I found one morning that it had shed its slough, but, not expecting this, made no notes. Python now measured 6½ ft.
"1. On Nov. 20th, 1897, at 7 p.m., Python entered the water in its zinc bath. Remained there continuously till 11 p.m. on Nov. 26th, when it shed slough in two large pieces in the water, and then left the bath.
"2. On Jan. 6th, 1898, at 3 p.m., Python entered water, and remained till 3 p.m. on Jan. 13th, when it cast slough in several pieces, and then left water.
"3. On Aug. 10th, 1898, Python again entered bath; remained without any intermission till 11.30 p.m. on Aug. 19th, when it left the water. At 11.40 it commenced rubbing its head forcibly on the felt which lines its case, frequently turning its head sideways to exert pressure upon the side of the jaws. When it had got as far as the nostril it gave two sudden and forcible expirations—not an ordinary hiss, but more like a sneeze, apparently to clear the loose skin from the inside of the nostrils; at all events it had this effect; then continued rubbing off the slough. At 11.48 the slough was completely free from the head above and below. At 11.52 I removed the bath out of the cage, as it seemed to have too little space. On being thus disturbed it ceased rubbing till 12.10, when it commenced to crawl slowly round the cage, pressing itself closely into the corners and along the sides. By 12.37 it had turned back two feet of slough, and at 1 a.m. three feet. At 1.30 a.m. the tip of its tail came away from the slough, which on this occasion was shed entire, but with one or two rents in it. During the last half-hour I assisted the process by allowing the Python to crawl through my partially closed hands.
"4. On Nov. 6th, 1898, Python entered water. Remained continuously till 24th, when it cast slough during the night.
"5. On Feb. 16th, 1899, Python appeared soon likely to slough, so I introduced its bath. It entered at once, but only remained a few hours, and kept on entering and leaving the bath until Feb. 25th, when sloughing commenced. As the slough was dry it did not readily peel off, and the process was only partially completed. The Python then entered the water, and remained till Feb. 28th, when it emerged and cast the rest of the slough. (On Feb. 27th it was observed to remain under water for seven and a half minutes once without raising its head for breath.)
"6. On July 18th, 1899, Python entered water, and stayed till July 28th, when it cast slough in water. The actual sloughing occupied one hour. (Cast whole, with many rents in it.)
"7. On Oct. 12th, 1899, Python entered water, and stayed till Oct. 26th, when it left water, and cast slough in several pieces.
"8. On Dec. 30th, 1899, Python entered water, and on Jan. 1st, 1900, cast slough in water in many small pieces.
"9. On March 24th, 1900, Python showed signs of sickening for sloughing, but refused to enter water. It tried to slough on April 2nd, but could only get off the scales on the belly. I accordingly fastened the Snake in the bath, where the rest of the slough came away on April 5th.
"10. On May 21st, 1900, Python entered water, staying till May 28th, when it left water, and cast slough in three large pieces.
"11. On Aug. 23rd, 1900, Python entered bath, stayed till Aug. 31st, when slough was cast in two pieces in the water.
"12. On Nov. 15th, 1900, Python entered water, stayed until Nov. 25th, casting slough in water in four pieces. The Python now measures just under 8½ ft. in length."
The foregoing admirably careful observations by Mr. Clarke show that his Python sloughed twelve times in three years, usually casting the slough in pieces, though in good condition. The term "sickening for sloughing" means the symptoms seen a few days beforehand, viz. roughness and darkening of the skin, refusal to take food, disinclination to move, and dimness of the eyes.
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