DEXTKIXK. 



DIABETB8. 



on December 15, the air-U-niperature was 4' i, tod that of the dew- 

 point 44-3, the depreeiion cMuequcntly. 2' 1. 



Th* mean air-temperature for the **me year wa* 51 -0, tad that of 



the dew-point 45'-8 ; UM depression S*'S. which U aUghtly below the 



.... . : ' . .' 

 In the Sikkiui ~ 



Himalaya, according to Dr. J. D. Hooker, the dew- 

 age of the year, U 49*'3, or 8' below the mean tempe- 



point, oo UM average 



rature of the air. In the dampest month (July) the mean dew point 

 u only eight-tenth* of a degree below the mean air-temperature, whilst 

 in December it sinks 10* below it. 



Profeesor C. Piaxzi Smyth found that no dew wa* formed on the 

 Peak of Tenenfle, at hi* astronomical observing station*. " In a region," 

 he sys, " where the avenge depression of the dew-point was, ai we 

 found it, the unheard-of quantity of 40*, and where it was not iiufre- 

 ouently above 50*, the formation of dew wu phyaically impossible." 

 ( PhiL Trans.' 1858, p. 478.) 



The determination of the dew-point and of iU depression being u it 

 were the indtjc of all bygrometry, a variety of methoda and processes 

 have been devised, and instrument* constructed for the purpose, or 

 virtually >, from the era of the Academicians del Cimento to that of 

 Daltun, and from his time to the present. This long and varied ex- 

 perience has resulted in the almost universal adoption of a method at 

 once simple and satisfactory the simultaneous observation of the dry- 

 bulb and the wet-bulb thermometers, an explanation of which will be 

 given in the article HTCROMETRY. The use of Daniell's hygrometer, 

 however, for this purpose, is continued by some meteorologists. 



The Vapour- Plane in the atmosphere, on which the clouds float, is 

 the superior limit of a stratum which is at the temperature of the dew- 

 point, at and below which cloud is continually forming, while it is as 

 continually being resolved into invisible vapour above. [CLOUD, 

 MKTEOBOLOGT, V.M-UI-B, VAPOUR-PLASH.] 



DEXTRINE (C,,H, O lo ). An isorneric modification of starch pro- 

 cured by boiling common starch in dilute sulphuric acid, and also in 

 tome other acids; by this treatment the starch soon loses its con- 

 sistence and becomes thin and limpid, being converted into ile.clrinc, 

 so called from its a.tiou on polarised light, in causing the plane of 

 polarisation to deviate to the right. When sulphuric acid is used, it in 

 to be saturated by the addition of chalk, and the liquor, filtered from 

 the sulphate of lime formed, is to be evaporated to dryness in a water- 

 bath. 



Dextrine thus obtained is a white gum-like mass, without any 

 appearance of crystallisation, soluble in cold water, and precipitable 

 from it by alcohol. Iodine is stated by some authors sometimes to 

 produce no change in the solution of dextrine, and on other occasions 

 to give a purplish red tint. The non-production of colour has, how- 

 ever, been stated to be a test of the perfect conversion of the starch. 



Dextrine may also be prepared by the action of an infusion of malt 

 kept some time at 150. Its composition is similar to that of starch. 



When the heat is continued after the formation of the dextrine, 

 this substance U converted into grape sugar, and thin effect ia produced 

 with great readiness. 



Dextrine, but not quite pure, is used by calico-printers as a substi- 

 tute for gum ; it is obtained by merely subjecting starch to the action 

 of heat, and thus prepared is known by the name of British gum. 

 [BRITISH GUM.] 



DEXTRO-RACEMIC ACID. [TABTABIC ACID.] 



DEY. The origin of the word dey is uncertain. Some have derived 

 it from the Turkish ddl, " a maternal uncle," and have supposed that 

 this designation was given to the chiefs of the states of Barbary to 

 eiui ess their almost paternal authority in the Ottoman empire, and 

 the high esteem in which they were held by the Porte. The name 

 is at all events of more ancient date than the Ottoman dominion in 

 northern Africa, since we find it used as early as the end of the llth 

 century as the title of the emissaries of the Assassins or Ismaelites. 

 The dignity of dey, or bey, of Tunis, Tripoli, and Algiers, wag borne 

 by the governors who were tributaries to the Turkish empire. Algiers 

 is now in the possession of the French, Tripoli is a pashalic of the 

 Turkish empire, and in Tunis alone does the title exist, though it 

 more frequently appears as pasha-bey. [ALUKRU. I/ ; TRIPOLI; 

 in GEOO. Div.] 



DIABETES, the discharge of a preternatural quantity of urine, the 

 chemical composition of which is also essentially changed. In tlim 

 AJMisr the urine U not only unusually large in quantity, but it is 

 either altogether destitute of several of it* constituent principles, or it 

 contain* them only in very minute proportions, while it acquires a new 

 ingredient, a quantity of sugar, which imparts to it a sweet taste 

 Medical writer* are not agreed whether the impregnation of the urine 

 with a sufficient quantity of saccharine matter to render it sweet to 

 the taste be absolutely essential to the disease ; it U therefore usually 

 divided into two species, namely, diabeta iiuipidtu, when there is dis 

 charged a preternatural quantity of urine which is perfectly iimipid 

 and iliabrtti mtttiliu, when the unusual quantity of urino whii-h i 

 voided U sweet to the taste. 



The diaeharge of a larger quantity of urine than natural, nnaltera 

 in its chemical constitution, may arise from numerous cause* of a 

 temporary nature, scarcely deserving the name of a disease, and cer 

 tainly not forming a disease of a speeifie character. The term diabetes 

 should therefore be restricted to that specific disease in which the 



secretion of urine it pretematurally increased, and it* chemical com- 

 xiaition at the same time essentially changed. 



In diabetes, properly so called, the urine i* generally so clear that it 

 appean at first sight to be entirely without colour ; but viewed in a 

 attain light, it i* seen to be slightly tinged with a yellowish green, or 

 t i* of a pale straw colour. Examined by the taste, it is almost in- 

 variably found to be more or lea* sweet ; and when chemically analysed, 

 t is ascertained to contain, usually in considerable quantity, a saccha- 

 rine matter, which ha* many of the properties of common sugar. It* 

 idour U likewise peculiar ; it is commonly compared to the faint odour 

 >f violets, or to that of sweet !. y or milk, Its specific graviu 

 noiily varies from 1-025 to 1-052. From a table given by Dr. Henry, it 

 appean that ten pounds of diabetic urine, at the average specific gravity 

 of 1 "040, yield* upwards of a pound and a quarter of solid extract. 



The quantity of urine voided in this disease is sometimes enormous, 

 [n one case on record, it amounted to the prodigious quantity of 52 

 wunds in the 24 hours ; but instance* are by no means uncommon in 

 which the quantity amount* to from 25 to 35 pound* every 24 hour* 

 for weeks or even months together. Although one of the mo.- 1 

 slant constitutional symptom* attendant on this disease is inordinate 

 thirst, yet the urine daily voided almost always exceeds the quantity 

 of liquids drank, and sometimes the whole of both solids and liquids. 



The diabetes commonly comes on slowly and almost imperceptibly, 

 at least without any such disorder of the general health as to attract 

 particular notice. It therefore sometimes exists a considerable time 

 before it becomes known ; and the change in the quality of the urine 

 is at length discovered by accident ; for its quantity may not at first 

 be very much increased, or if increased to such a degree as to attract 

 notice, the circumstance is usually attributed to some temporary cause. 

 At length, however, the constitution manifestly suffers ; the strength 

 and vigour foil, the patient feels languid and indisposed to make any 

 physical exertion, the mouth ia dry, the tongue clammy ; there is un- 

 usual thirst; a slight degree of fever is set up, indicated by alternate 

 chills and heats ; but the most remarkable circumstance is a change in 

 the condition of the skin, which becomes dry, harsh, and sometimes 

 even f urfuraceous, or apt to peel off in scales. The thirst now increase* 

 to such a degree a* to be evidently morbid ; this is often, though not 

 always, accompanied with voracious appetite; and the quantity of 

 urine discharged not only decidedly but steadily increase*. If the 

 observation of those circumstances should lead to the examination of 

 the urine, it is found to be sweet to the taste and of a light green or 

 pale yellow colour. The patient meantime is commonly observed to 

 have lost flesh, and is troubled with a sense of heat and pain in the 

 region of the stomach, with aching in the back and loins, and uneasy 

 sensations in the course of the urinary passages. The bowels are 

 usually costive, the breathing short and oppressed, with a dry tickling 

 cough, and the pulse U commonly frequent. As the disease advances, 

 all these symptoms increase in intensity ; the tongue becomes either 

 loaded with a dark-coloured fur, or unnaturally clean and of a dark or 

 purplish red colour ; the thirst is more urgent ; the appetite, formerly 

 voracious, is now perhaps abolished or depraved ; the bowel* ore more 

 constipated ; the skin more harsh and scaly ; while the urine, increas- 

 ing in quantity, becomes still more altered in quality. At length 

 there come on headache, giddiness, occasional loss of vision, impaired 

 memory, and diminished mental energy. The debility and emaciation 

 steadily increasing, the patient sinks with many of the symptoms of 

 hectic fever, or is suddenly cut off by consumption, dropsy, apoplexy, 

 or some other incurable disease established in some vital organ. 



From the preceding account it appears that this disease is generally 

 of a chronic character; but it sometimes attacks in on acute form, the 

 marked symptoms of the malady coming on suddenly in a previous 

 state of apparent health, and proving fatal in a few days. This, how- 

 ever, is very rare. It seldom runs its course under some months, and 

 it sometimes lasts several years. It frequently disappears for a while, 

 especially under proper treatment, and then recurs after the lapse of a 

 few mouths or years ; so that the relief obtained is commonly only 

 temporary, the disease resuming all it* severity from a slight exposure 

 to it* exciting causes, or from any considerable deviation from the 

 proper diet and regimen. Hence it is perhaps the prevalent opinion 

 ;MH"IIL; physicians that it is absolutely incurable. There cannot be a 

 question that by appropriate remedies and great and persevering care 

 on the part of the patient, it is capable of being very much relieved, 

 and even of being altogether suspended for an indefinite nun. 

 yean. The evidence of this is indubitable; but it is more doubtful 

 whether it con be permanently and radically cured. 



An inspection of the organs after death does not throw so much light 

 on the seat and nature of diabetes as might have been expected. In 

 even] coses in which the symptoms were present in a very intense 

 degree during life, no appearance of change of structure in the urinary 

 organs could be detected after death. In general, however, the kidneys 

 are larger than natural ; more turgid with blood ; more flaccid ; softer, 

 and more easily torn. Sometimes, though rarely, they are found in the 

 contrary condition, smaller and harder than natural, and their uu-m- 

 branous envelope and their cortical substance, are of a cartilaginous 

 firmness and density. Several observe have recorded the remark- 

 able fact, that the organic nerve* which supply the kidneys are greatly 

 enlarged in size. The ureters are commonly dilated, and the urinary 

 bladder is often thickened. It is obvious that these mordid states of 



