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IX.—Some Observations on the Cuticle in relation to Evaporation

Published online by Cambridge University Press:  17 January 2013

John Davy
Affiliation:
London and Edinburgh.

Extract

Though it is generally admitted that the cuticle performs an important part in retarding and regulating evaporation from the surface of the body, yet I am not aware of any inquiry hitherto made to determine the fact with exactness.

On account of the importance of the subject, I have been induced to engage in it. The experiments instituted for the purpose have all been of a very simple kind and easily made. They were on the similar parts of dead animals, detached immediately or very soon after the animals had been killed. From one specimen in each instance, the cuticle with the cutis, or the cuticle alone, was removed; whilst from the other these parts of the integuments were left entire. Each was carefully weighed, and then suspended, exposed to the air, side by side. Day after day, with occasional interruptions, or hour after hour, the weighing was repeated, and the result in the loss sustained was noted down. The experiments were made, when not otherwise mentioned, as just described, in a room in which, except in the height of summer, there was commonly a fire by day, its temperature during the day and night varying from about 50° of Fahr. to 55° and 58°. The animals affording the subjects of the trials were the trout, frog, toad, hare, rabbit, pig, thrush, common fowl, blue tit. Even at the risk of tediousness, I shall give the results of the weighing in some detail,—exactness in such trials being the first thing necessary.

Type
Transactions
Copyright
Copyright © Royal Society of Edinburgh 1865

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References

page 117 note * A simple experiment illustrates this. Two portions of recently killed lamb were selected. One (No. 1) weighing 168·5 grs. was suspended by a thread, freely exposed to the air of a room varying in temperature from 60° to 65°, i.e., the day and night temperature. The other (No. 2), weighing 160·1 grs., was suspended hanging free in a small glass receiver, in which was a little water, and was so covered as to allow ingress of air, and yet almost to prevent any evaporation. The results were strongly marked. No. 1 lost weight rapidly, and soon became hard and dry without acquiring any putrid taint. No. 2, on the contrary, softened and actually liquefied, at the same time becoming extremely putrid. In an experiment similarly conducted over water—but the water exhausted of air and in vacuo—the muscle escaped putridity. This, from the 11th July to the 20th August, illustrating in addition, I may remark, the difference as regards tendency to putrefaction between muscle and blood; the latter, as I have shown elsewhere (p. 25 of this volume), undergoing the putrid decomposition, even in vacuo, being impregnated with oxygen.

page 118 note * Nouveau Voyage aux Isles de l'Amerique, &c. Par R. P. Labat. Tom. iii. p. 132.

page 118 note † When dry, even muscle no longer attracts the flesh-fly; it is the moist putrefying flesh which allures it, that being alone suitable to the development of its ova.

page 118 note ‡ A specimen of pemican (for which I was indebted to Sir John Richardson), about twelve months old, of the best quality, I found composed of—

84·88 fat,

11·77 muscular fibre chiefly,

3·35 water.

The fat consisted of oleine or elaine chiefly, and stearine. The muscular fibre, moistened, was found unaltered as to striated structure.

page 118 note § In 1852 I put by, merely wrapped in paper, portions of pork, mutton, beef, fowl, common trout, pollack (Gadus pollachius). They were left in the drawer of a table, in a room in which, during three-fourths of the year, there was a fire. Examined in December 1864; in all of them, with one exception, the muscular fibre exhibited the original striated structure distinctly. The exception was that of the trout, in the muscular fasciculi of which the strise were less distinct Pemican, which had been kept two years (a portion of that of which the composition is given in the preceding note), exhibited the striated muscle with perfect distinctness.

To what extent these portions of meat and fish might otherwise be altered, and their nutritive quality impaired, is a question I am not prepared to answer. I may mention that white of egg, which, on thorough desiccation at a low temperature, is again for most part soluble, appears, if long kept, to become insoluble, judging from a trial of some put by after desiccation in 1852, and recently examined.

page 119 note * Now, August 5, No. 1, where least exposed to light, has become greenish; where most exposed, brownish green.

No. 2 has become dark brown, almost black, and has acquired a crescentic form, contracted, without being shrivelled.

No. 3 has become of a light brown, and is much shrunk and shrivelled.

page 119 note † Now, September 10, on No. 1, three small greenish sprouts have appeared, tipped with black; general hue the same. Nos. 2 and 3 of the same colour and appearance as before.

page 119 note ‡ Now, December 1, the sprouting buds of No. 1 have grown a very little, showing a very feeble vitality, and very slow progress. In Nos. 2 and 3 no apparent change.

page 119 note § Now, February 2, the bud of No. 1 has grown into a stalk, with terminal greenish leaflets, and three lateral long roots, with delicate spongioles.

page 119 note ∥ Now, March 14, the tuber No. 1 is slightly shrunk; the stem from it is ·9 inch in length, and ·3 inch in diameter where thickest; is of a dark purple, and is surmounted by several small green leaflets; the roots from its side, numbering five, vary in length; the longest is 1·7 inch. Weighed again on the 28th of May, the tuber was only a little more shrunk; it was reduced to 161·5 grs. The growth from it, the stem, leaflets, and other offshoots, had all a healthy appearance.

page 120 note * In another experiment, begun on 27th October 1863, the results were much the same, with this difference, that, on the 17th March 1864, the unpeeled potato was removed from the light into a dark cupboard, and covered with a small inverted porcelain jar. There it has vegetated; it has shot out many branches, all but the largest of which are white; it is of a light purple; attached to them are many well-formed tubers. Now, March 15, 1865, the weight of the potato is reduced from what it was at first, viz., 900·5 grs., to 331 grs. It has no terminal leaflets. There are seventeen small tubers connected with it; all are of an oval form, like the parent tuber; the largest is ·4 inch in length. All of them are throwing out shoots, and they are most easily detached.

page 120 note † Its weight afterwards fluctuated a little, according to the hygroscopic state of the atmosphere.

page 120 note ‡ Sliced apples exposed to the air dry rapidly, as do also sliced potatoes and carrots; and if put up in paper bags in a dry place, they will keep fit for use for a long time. No vegetable that I am acquainted with undergoes change more rapidly than the sweet potato (Batatas edulis), yet when sliced and dried, as I have found by experience, it may be kept for years unaltered. I have some thus preserved, which I brought from the West Indies in 1848.