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that with due attention they may be seen anddemonstrated in some brains, by persons whoare acquainted with the ordinary anatomy ofthat organ. It must be regretted, that inaddition to the misinterpretation of the pas-sage quoted by Dr. Macartney, there shouldalso have been a misapplication of the con-cluding paragraph, which error might havebeen avoided on his part, by first ascertain-ing if it were written with reference to him.I am, Sir, your obedient servant,
Dublin, Sept. 27, 1841.THOMAS MOORE.
AMALGAM FOR STOPPINGDECAYED TEETH.
J. IJf. supplies the following answers tothe three queries proposed by Mr. LINTOTT,in THE LANCET of Sept. 18th:—
It is probable that metals are capable offorming definite compounds by uniting witheach other in one or more atomic proportions ;and when mercury is one of the metals, thecompound is called an amalgam. But littleis known of this class of alloys; Klaprothhas analysed the crystallised amalgam of
silver, and found it composed of mercury64 parts, silver 36; which numbers corre-spond so nearly with 202 and 108, or theatomic weights of mercury and silver, thatwe may conclude there is an equivalent ofeach metal present, or one of silver to two ofmercury, if we take the atomic weight ofmercury at 101, as Graham proposes.This amalgam may be dissolved in excess
of mercury, and an apparently fluid amal-gam result. When the solvent is not in toogreat excess the amalgam will crystallise.This takes place more rapidly if part of themercury be removed by straining throughchamois leather, when it quickly becomeshard, and of a dull-white colour, owing tothe rapid crystallisation of the amalgam.When common salt comes in contact with
this amalgam, the chlorine of the chloride ofsodium will act upon the silver, formingchloride of silver, which readily darkens onexposure to light ; and the mercury being leftin the state of fine mechanical division, is eitheroxidised, or converted into calomel or corro-sive sublimate, by fresh chloride of sodium,and as such will be absorbed, and exert itsusual effect upon the system.These effects would take place from the
presence of common salt alone ; a substanceof such constant and extensive use, that wemay regard it as almost always present inthe saliva. It is obvious that there are
many other agents whose action would beprejudicial, but I have taken salt for thesake of illustration.
Mansfield, Sept, 23, 1841.
UNIVERSITY OF LONDON.
WE are requested to state that the SecondExamination for the Degree of Bachelor ofMedicine in this University will commence,in future, on the first Monday in November,in place of the third Monday in July.
A Concise and Practical Treatise on thePrincipal Diseases of the Air-Passages,Lungs, and Pleura. By Alfred Catherwood,M.D., C.M. London : Duncan and Mal-colm, 1841, 8vo, pp. 208.
FRESH-WATER INFUSORIA.—(From a Cor-respondent.)—H. L. is much interested in thestatement of Mr. Dalrymple respecting thehabitats of some of the fresh-water infusoria.Will Mr. D. obligingly state, through themedium of THE LANCET, if he has obtainedliving xanthidia from any of the watersaround London ; and if so, where they maybe procured? The abundance of the loricæ,or cases of the genus xanthidium in somefluids is such, that it becomes important toascertain what relation exists between therecent and fossil species. At Clapham thestephanoceros is very rare ; it is not grega-rious ; the animalcule is generally foundsingle, or seldom more than two individualson the same leaf or twig have been found. Ihave hunted for hours, and obtained but onespecimen.Our correspondent, Mr. T. M., will pro-
bably admit that however proper it was forhim to write the parts of his letter which wehave omitted, it would not be proper for usto print them. We had already taken theliberty of omitting what appeared to be someimpertinencies in the letter that preceded hisown.
Mr. S. (Epsom).—Just at the presentmoment we have not room for a third con-troversialist on the subject of the letter datedSept. 27th.
Dr. Duigan’s letter in the " AustralianChronicle ;" Mr. Wadd’ington’s circular; theletter of Mr. Orton the paper of Dr. TVill-shire; and the remarks, Shade of Smellie,
have been received.Mr. Levison’s letter, received.! Erratum.—In the letter of Mr. Camden,p. 31, line 5 from the bottom, the quotationfrom the " Cyclopaedia of Anatomy, ! ? whichstands thus-‘° Fracture is uncommon in in-
fancy and in childhood; the bones bendingrather than breakimg"—should have been
pointed thus : " Fracture is uncommon in
infancy ; and in childhood the bones, bend.ing rather than breaking, &c."