One end of the bell's cock communicates with the atmosphere, the other with the receiver-plate R. This is of glass 2 inches in diameter, 0.75 thick, and is cemented on the top of the iron pillar P. Through it are drilled the passages shown in fig. 3; in t is ground the glass tube, shown in fig. 1 by T, the end of which is in contact with the cock, and their junction made air-tight by a tube of Para caoutchouc; in g and k are similarly ground the siphon-gauge G and the glass cock K. These all communicate with the receiver by the passage v, and by removing the tubes can be easily dried or cleaned. The cock K is connected by elastic tube with the catch-jar N, which is supported in a small mercurial trough M.

The operation of this machine as an air-pump is as follows:-The receiver being placed on R, open the screw $, press down the plunger nearly to the bottom of the cylinder, remove the key of the bell-cock, and pour through the opening which it leaves as much mercury as will fill the bell to the bore of the cock. In this one 10 lbs. are required. Raise the plunger to the top, and the metal will subside from the bell till only 0.3 of an inch remains on the top of B, filling the space left vacant in D by the rising of the plunger. The length of the plunger and the height of B must be adjusted to this condition. Replace the key; turn it to communicate with the atmosphere (which position I call (a)), and depress the plunger. The mercury will rise again in the bell, filling it, and expelling the air from it, till at last a little mercury will appear in the bore of the cock. To prevent this from being splashed about, a bit of bent tube v is ground on the end of the cock, which receives it, and when it has too much is removed and emptied into D through S. Secondly, turn the key to shut off the bell (position (o)); draw up the plunger, close S, open E, and couple it to an air-pump, with which exhaust D. This pump may be of the commonest description, for an exhaustion of one or two inches is quite sufficient. The mercury will sink in the bell, leaving above it a Torricellian vacuum. Close E, and turn the key to communicate with the receiver (position (r)); its air or gas will expand into the bell.

These three operations form the cycle of operation, and must be repeated till the required exhaustion be obtained, with one modification of the first one. In it, at the second and all subsequent strokes, the key is to be at (0) and S opened; thus the atmospheric pressure will raise the mercury and do much of the plunger's work; that must then be depressed and the key set at (a); the other two steps are as at first.

When the instrument is to be used as a gas-holder, either the receiver must be in its place, or the opening of R must be closed by a piece of flat glass; the bell must be filled by the plunger, and made, by (r) and by opening k, to communicate with the jar N. The mercury will rise in that to its neck, and sink in A; fill A again, pass gas into N, and, by carefully working the key, draw it into A till that is full. As this gas will be mixed with the air of the vessels and passages, it must be expelled, and A refilled till its purity is certain. If it be noxious, it must be conducted into some

absorbent fluid by an elastic tube, slipped on the a end of the cock; which will also convey the gas to any vessel.

If it be required to fill a receiver for experiments in an atmosphere of gas either at common pressure or a less one, it may either be exhausted by an air-pump connected with K, and filled from A, or exhausted by A and filled from N. The former can only be done with gases which have no action on brass.

These operations seem complicated when described with so much detail, but in practice they are very easy, and their result is good. Some precautions, however, are required to ensure it. The bottom of the bell-cock and of its key must be ground, so as to leave no shoulder or hollow in which air may be entangled when the bell is filled. Every part of the metal work must be air-tight; this can only be secured by covering, not only its joints, but its whole surface with several coats of varnish-paint— best of white lead. When the first coat is applied, on exhausting the apparatus, every hole or pore is revealed by an opening in the paint (often almost microscopic), which must be filled up as it forms till all is tight. It is almost needless to mention that the whole must be perfectly dry. If the bell be filled a few times with undried air, enough of moisture will adhere to its walls to prevent an exhaustion of more than 0.1 inch. In such a case it must be dried by drawing air into it through sulphuric acid, and this repeatedly. Moisture also occasionally finds its way into a part still more troublesome, into the passage which connects the bell and cylinder; it is probably condensed there when the mercury is colder than the atmosphere. I remove this by connecting the tube of K with a desiccator; setting C to (r), opening K and E, and by working the air-pump drawing a stream of dry air into D, which bubbles up through the mercury in the passage, and at last sweeps away all trace of water and its vapour. In this operation it is necessary to remove a portion of the mercury, as otherwise it would be sucked into the pump; indeed this mischief might occur in ordinary work by some mistake in the manipulation-for instance, by leaving open with (a). To prevent the possibility of this, D is connected with pump by a mercury trap, easily imagined, which intercepts any of that metal that might come over. And lastly, the interior of the bell must be perfectly clean if the highest degree of exhaustion is required. This state is obtained by washing it with strong nitric acid, then with distilled water, and when quite dry wiping it with linen, from which all traces of soap or starch have been removed by boiling it in rain-water. Thus we reduce to a minimum the film of air which adheres to the bell even when filled with mercury, and lessens its vacuum. When all these precautions were taken, I found that with a receiver containing 3.7 inches, the fifth operation brought the gauge (which had been similarly cleaned and carefully boiled) down to 0.01. The sixth brought it still lower, but my present means of measurement* are not sufficient to determine the precise amount. In this * A micrometer microscope put in the place of the telescope of my theodolite.

E

1

3.7

17'

machine the old air-pump theorem ought to hold, and by it, with the fraction I find that the fifth should give 0·007, and the sixth 0·0014; so that the presence of adhering air is still sensible, though very slight. So high a power, however, is not long maintained; for by use, and especially with oxygen, which (probably from the presence of ozone) has a peculiar tendency to dirty mercury, the bell becomes soiled; but it continues to give a vacuum of 0.02, which is quite sufficient for ordinary objects. At common pressure and temperature, the electric discharge through the receiver shows no evidence of the presence of mercurial vapour; but at 0-02 it is otherwise; the discharge is greenish white, and the spectrum shows little except the lines of mercury. If the gauge were detached, perhaps this vapour might be absorbed by gold-leaf.

The apparatus acts well as a mercurial gas-holder, and can deliver 18.5 inches. Like all other contrivances for confining gaseous matter by mercury, it is liable to have its contents contaminated with air by diffusion between the metal and the vessel which contains it; but I expected that in this arrangement the defect would be little felt. In order that it may take place, the air must pass a distance of 17.2 inches, of which 14-6 is a tube only 0.125 in diameter, and the rest is in a vertical direction against the pressure of 2.6 inches of mercury. A single experiment will show how far this avails. The bell was filled with dry hydrogen, which was found to contain 0.901 of the pure gas; it was left for ten days exposed to considerable changes of temperature, and was then found to have 0-854; it was therefore contaminated at the rate of 0.005 per day. I am not aware of similar measures with ordinary mercurial apparatus; nor is this amount of error very important; but it may I believe be corrected by a means long since announced by the late Professor Daniell which has been strangely neglected. He proposed it to prevent the infiltration of air into barometers. If the liquid metal adhered to the surface which it touches, as water would, this action could not occur; now it wets, if I may use the word, several metals, as copper or silver, but it also dissolves them, and becomes less fluid. Daniell, however, found that it does wet platinum without acting on it in any injurious degree; and advised that a ring of platinum wire should be fused round the tube where it dips into its cistern. On inquiring of his friend and fellow-labourer, Dr. W. A. Miller, I learn that it was completely successful, but was not taken up by the opticians, and passed out of memory. It is obvious that if a bit of platinum tube were cemented in the vertical passage below D, it would effectually bar the diffusion. I do not like to undo the joint there, which is now perfectly tight; but I will certainly, when the opportunity offers, try the experiment.

X. "On the Distal Communication of the Blood-vessels with the Lymphatics; and on a Diaplasmatic System of Vessels." By THOMAS ALBERT CARTER, M.D., M.R.C.P., Physician to the Leamington Hospital and Warwick Dispensary. Communicated by W. S. SAVORY, Esq. Received June 2, 1864.

(Abstract.)

In this paper the author has recorded the results at which he has arrived concerning the distal intercommunication of the hæmal with the lymphatic system by means of injections thrown into blood-vessels; he also describes certain minute vessels and networks of vessels which can be shown by the same means to exist in certain mucous membranes and elsewhere. These he has named diaplasmatics.

The author's attention was first particularly called to the relation which the lymphatics bear to the blood-vessels, by observing that when the latter are fully distended with a very penetrating injection, such injection often finds its way into the lymphatics without the occurrence of ordinary extravasation.

He has thus injected the livers of three human beings and of three pigs from the portal and hepatic vessels, the former (vessels) being filled with Turnbull's blue precipitated in gelatine, and the latter with carmine similarly treated; and in each instance he has found that the injection had gained entrance to the superficial lymphatics.

In sections taken from the surface of the pig's liver, these vessels (which may readily be distinguished from the blood-vessels by their knotted irregular appearance and rapid increase and diminution in size) are observed in many instances to surround a lobule, throwing out loops and prolongations towards its centre. A certain number of these prolongations, both in the human liver and in the pig's, when traced are seen to diminish in size so much as to be considerably less in diameter than the capillaries of the organ, in which they appear to lose themselves or rather originate. Their commencements in this part, it is acknowledged, are extremely difficult to determine by simple inspection, on account of the underlying capillaries being filled with injection of the same colour; but in some instances (as, e. g., where the pigment in the capillaries has faded) the author believes that he has seen the actual anastomoses of the two sets of vessels. The circumstance, however, which renders exact microscopic observation so very difficult, is the one which affords the best evidence of the communication of the two systems, viz. that the minutest lymphatics are almost invariably filled with injection of the particular tint seen in the capillaries in close relation to them. Thus if the capillaries be red or blue, or any of the intermediate shades of purple, the smallest lymphatics in the immediate neighbourhood will be of a precisely similar colour; which would appear distinctly to show whence the lymphatics derive their supply of fluid.

A human thyroid body which the author injected with carmine and

gelatine from the blood-vessels, also exhibited a phenomenon similar to that observed in the organs just mentioned.

Sections taken from this gland and examined with the 4-inch objective, showed that from the capillaries are given off fine processes which break up into a network among the cell-elements of the vesicles, and, furthermore, that this network is in communication with the lymphatics which lie in the intervesicular parts of the gland. In addition to this, however, there are communications between the capillaries and lymphatics in the stroma itself. The processes which emerge from the capillaries in the stroma of the thyroid as well as in the fibrous tissues of other parts, such as the membrana nictitans of the cat, bear a very strong resemblance to connective-tissue corpuscles; and such the author considers them to be in these parts. as these tubular processes can be shown by injection to form a plexus in the retina (cat), to be connected with the nuclei of the capillaries, the corpuscles of bone (perch and mouse), and the fusiform bodies found among the fibrilla of muscle (frog), as well as with the cells of connective tissue and its modifications, it has appeared that the whole of these structures belong to one system of vessels. This system the author has named, provisionally at least, "Diaplasmatic," because, on account of the extreme minuteness of its channels, it can only allow of the passage of the liquor sanguinis.

But

To designate the whole of these minute vessels lymphatics would, he considers, at the present time be somewhat premature, because those of muscular fibre and of bones, and others which will be mentioned immediately, have not been observed to join recognizable lymphatic trunks; and moreover it would seem by no means improbable that some of them may both commence and terminate in the blood-vessels, thus constituting what might be styled an intercapillary plexus; or they may even have a triple connexion, viz. with the arterial capillaries, the lymphatics, and with the venous capillaries or the veins.

The position in which the diaplasmatic network may be most readily demonstrated, both with and without injection, is in the mucous membrane of the palate of the frog or toad. In this part, when the viscid mucus and the ciliated epithelium have been removed, there may be seen with the 4-inch objective, a very minute granular nucleated network, in each mesh of which is placed a globular nucleated cell. The membrane consists, therefore, of three layers—of a superficial ciliated layer, next of a granular nucleated plasmatic network, and lower still of a basement layer of globular nucleated cells. The processes of the middle granular plexus extend not only in the horizontal direction, but also upwards between the ciliated cells, and downwards between those of the basement layer, where they become continuous with the blood-vessels lying in the fibrous tissue beneath. This connexion with the blood-vessels, the author says, he has been able to make out by means of injection in the palate and oesophagus of the frog and toad, as well as in the mucous membrane of the eyelid of the latter animal.