nere trace of amyloid substance can be detected, and that only in the cells of the bulb. If a number of embryo lambs, of various sizes, are placed ide by side, and a drop of a weak solution of iodine acidulated be allowed o fall on a corresponding part of each, the peculiar brown stain produced vill be seen to increase in intensity up to a certain point. After the appearance of the hair, the stain gradually diminishes in intensity, showing the essening quantity of amyloid substance in the tissue. If the tails cut off rom a series of foetal lambs are placed in a vessel containing a very weak solution of iodine acidulated, it illustrates (by the colouring) very strikingly the increasing abundance of the amyloid substance in the epidermic tissue up to a particular period (that is, when the hair is fully formed), and then its gradual disappearance. The feet and hoofs similarly treated illustrate the same for the horny tissue of this part. From the time that the fœtus of the sheep is nine inches in length (at which period the amyloid substance seems to be at its maximum), the amyloid substance contained in the horny structure of the hoof gradually diminishes until shortly before birth, when, even after prolonged boiling, scarcely a trace can be extracted from it.

In the tissue of the lung of mammalian embryos, the amyloid substance is at one period present in immense quantity. After the watery part is driven off by evaporation, more than 50 per cent. of the dry residue is found to be nothing else than animal dextrine. As the organ approaches maturity, and the animal is about being born, but before it has yet drawn a single breath, the amyloid substance is found to be reduced to a very small quantity indeed, and in some instances to have absolutely disappeared. The following Table shows the progress of this change in the lung of the embryo of the sheep, and, I believe, very closely represents the corresponding amount of change which takes place in the lung-tissue of other embryos which I have examined, viz. of the rabbit, cat, dog, cow, rat, guinea-pig.

It would be no very easy matter to attempt to indicate precisely the condition of development of the embryo at which the maximum amount of amyloid substance is to be found in the tissue of voluntary muscle; in embryos of apparently the same age and condition of development it is found

to vary a good deal in amount. But this much may be asserted positively, that for some time before birth it has much diminished in quantity in this tissue, although always existing in it in notable amount up to and after birth. After repeated examination of various embryos, I believe I may state that the following Table, made from examination of the voluntary muscular tissue of fœtal lambs, correctly represents the average quantity of animal dextrine found in this tissue at various periods of its growth*:

It appears therefore that, although it exists in a less proportion than at an earlier period, there is in muscular tissue at the period of birth a considerable quantity of amyloid substance; and this does not disappear altogether for some time in lambs, occasionally not for some weeks after birth. The tissue of voluntary muscle cannot be considered to have attained maturity at the time of birth; it has as yet hardly been called upon to exercise its functions. There is, however, a muscular organ the tissue of which commences, of necessity, the active exercise of its functions at an earlier period than that of voluntary muscle. The muscular structure of the heart, so far as its functions and activity are concerned, attains maturity

* It was stated in my former communication that 3.5 grains of amyloid substance was obtained from 60 grains of muscular tissue of a fatal calf; but this was not quite pure, the investigation not being made with so much care as in the present instance.

earlier than other muscular tissue. The relation which the amyloid substance bears to it is therefore of much interest. In all embryos, without exception, which I have had an opportunity of examining at a time when they were closely approaching the period of birth, there has been no more than a trace of amyloid substance remaining in the muscular structure of the heart. The preceding Table, drawn up from examination of the heart of the embryo of the sheep, closely represents the corresponding state in other embryos.

The liver, which is the organ destined to form the amyloid matter during adult life, naturally has an increase of this material going on in its tissue up to and after birth: it does not make its appearance in the liver until the embryo is already well advanced in development; it then is found gradually and very slowly to increase in amount, but even at the time of birth is present in comparatively small quantity (2 per cent. in the liver of a lamb 20 inches long).

The rapidly growing horn of a young stag was not found to contain any amyloid substance in the tissues, neither does it exist in the texture of the growing horn of the calf; it is not found in the hair-bulbs of the adult, neither is it to be discovered as a formative material of the newly formed muscular fibres of the uterus when this organ is undergoing its remarkable reconstruction after delivery.

What is the function of this material during foetal life? It can at least be said it does not change into sugar, neither does it give rise to fat. It seems to be a formative material, which, gradually becoming united with nitrogen, gives origin to the azotized structures.

IX. "Description of a New Mercurial Gasometer and Air-pump." By T. R. ROBINSON, D.D., LL.D., F.R.S., &c. Received June 2, 1864.

In some experiments on the electric spectra of metal and gases, I felt the want of a mercurial gasometer for working with such of the latter as are absorbable by water. That of Pepys is on too large a scale for my requirements, and it seemed better to contrive one more easily manageable, which I saw could also be made to act as a mercurial air-pump. In this I have succeeded to my satisfaction; and I hope that a description of it may be useful to those who are engaged in similar researches.

There have been several attempts made to exhaust by means of mercury, the chief of them with which I am acquainted being those of Close (Nicholson's Journal, 4to, iii. p. 264), Edelcrantz (Nicholson, 8vo, vii. p. 188), Traill and Children (Nicholson, xxi. pp. 63 & 161), and that of Geisler, which he uses in preparing the beautiful vacuum-tubes which bear his name. In all the principle is the same. A vessel is filled with mercury, which is made to descend from it, leaving in it a Torricellian

vacuum; this vessel may be made to communicate with a receiver, and abstract from it a portion of the gas which fills it; and by repeating the process the receiver can be exhausted as by successive strokes of an airpump. In the two first instruments to which I have referred, the descent of the mercury is produced by lifting a plunger which fills one leg of an inverted siphon, the vacuum vessel being at the top of the other leg. On depressing the plunger, the mercury is again forced up to fill that vessel; and of course both legs must be longer than the barometric column. In the two next, the receiver itself is filled with mercury, which, by opening a cock, falls through a tube of sufficient length into a cistern below. Here the stroke (so to call it) cannot be repeated. In Geisler's the bend of the siphon is of vulcanized caoutchouc, so that one leg can be inclined down to a horizontal position, and thus allow the metal to fall from the other, or when raised to the vertical position fill it again. This I believe acts well, but it must be rather unwieldy; and my practical acquaintance with the working of tubes of that material has made me suspicious of their tightness and permanence under such circumstances.

As in all these cases the mercury is supported in the vacuum-vessel by atmospheric pressure, it is obvious that its descent will be produced by removing in any way that pressure; and an effective means of doing this is supplied by the common air-pump; more tedious certainly than the mechanical means above mentioned, but far more manageable; and as any mercurial pump must be slow in its working, while it is only required for spe cial purposes, this defect is not of much importance, and moreover is compensated by some special advantages.

But besides bringing down the mercury, means must be provided for raising it again. My first plan was to do this by condensed air, the same syringe which made the exhaustion having its action reversed by a wellknown arrangement. It worked extremely well, was lighter, and required less mercury than the contrivance which I finally adopted; but it is less convenient for gasometric work, as the syringe must be worked while gas is delivered. The machine in its present form is shown in fig. 1. Its base is a stout piece of mahogany, 21 inches by 10-5, with a rim round it 0.5 deep to prevent the loss of any spilled mercury, and handles at the ends by which it can be transported. To this is firmly fixed the iron stand B, 3-5 high, 4 in diameter above; its upper surface is carefully trued to a flanch, in which is cemented the vacuum-bell A, so that when the touching surfaces are lightly smeared with a mixture of lard and wax and screwed together by the six screws (some of which appear in the figure), the joint is air-tight. The bell A is 2 inches in diameter and 6·5 high; it has a tubulure at the top, in which is ground a glass cock C, whose construction is shown in fig. 2. The key of it is pierced from its bottom to a level with the bore, with which this perforation communicates occasionally by a lateral opening. In the position of the figure, it will be seen that the bell communicates with the branch a; if the key be turned half round, it is connected with the

branchr; and in an intermediate position it is completely shut off. These glass cocks have this great advantage over those of metal, that it can always

be ascertained if they are air-tight; their transparency permits us to see if the key and shell are in optical contact; and the slightest air-way there is at once detected. They should not be lubricated with oil, which grips, and may perhaps find its way into the bell and soil its interior. I find the best material to be castor oil with rosin dissolved in it. A hole is drilled down the axis of B, which communicates by a tube (sunk in the wood and therefore not visible in the figure) with the cast-iron cylinder D. This is 13 inches high and 3.2 in internal diameter; its top and bottom are secured to it air-tight by screws; in it works a plunger of boxwood well varnished 10-4 high, and moving so loosely that mercury may pass it easily. The plunger is wrought by a rod passing through the collar of leather H. In the top of the cylinder is a stopcock E, to which is fixed a tube of vulcanized caoutchouc (varnished with a solution of caoutchouc in benzidine), which is shown hanging down; it has a coupling to connect it with an ordinary air-pump. There is also in the top a screw S for admitting air.

VOL. XIII.

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