DEW-BERRY. 



DIBBLE, 



temperature at each hole is taken, by the same 

 thermometer, or by two thermometers, and the 

 proportional part of the difference correspond- 

 ing to the distance of the dew-point line from 

 the lower thermometer is added to the tempera- 

 ture observed by it. Care should be taken in 

 making this observation to let the temperature 

 of the different parts of the bar become sta- 

 tionary before attempting to register them. In 

 another form of the instrument, an iron or 

 copper trough containing mercury is substi- 

 tuted for the bar; one side of the trough, which 

 is best made square in its section, is of polished 

 steel or gilded. The trough is attached to a tin 

 vessel, as in the other instrument. When the 

 surface is cooled down so as to obtain the line 

 of deposit on the face of the trough, the bulb 

 of a small thermometer, which may be moved 

 along in the mercury within, is brought oppo- 

 site to the line. The temperature which it de- 

 notes is, of course, the dew-point. See ATMO- 

 SPHKRK and HYG.ROMKTER. 



DEW-BERRY. The fruit of the blue bram- 

 ble (Rubus ms), so termed from the resem- 

 blance of the glaucous bloom, or waxy secre- 

 tion upon the black shining berries, to dew. 

 (Eng. Flor. vol. ii. p. 409.) See BRAMHLE. 



DEWLAP (from lapping or licking the 

 dew). A term applied to the membranous 

 fleshy substance that hangs down from the 

 throats of neat cattle. 



DEY. An old English word for milk, now 

 obsolete, but from whence we derive dairy. 



DIARRHOEA. See DISEASES OF SHEEP, CAT- 

 TLE, and HORSES. 



DIASTASE. When cold water is poured 

 upon barley newly malted and crushed, is per- 

 mitted to remain over it for a quarter of an 

 hour, is then poured off, filtered, evaporated to 

 a small bulk over boiling water, again filtered 

 if necessary, and then mixed with much alco- 

 hol, a white tasteless powder falls to the bot- 

 tom, to which the name of diastase has been 

 given. 



If unmalted barley be so treated, no diastase 

 is obtained. This substance, therefore, is 

 formed during the process of malting. 



If wheat, or barley, or potatoes, which by 

 steeping in water yield no diastase, be made to 

 germinate or sprout, and be afterwards bruised 

 and treated as above, diastase will be obtained. 

 It is therefore produced during germination. (J. F. 

 W. Johnston's Lectures.} 



Diastase, like sulphuric acid, possesses the 

 property of transforming starch entirely, first 

 into gum, and then into grape-sugar. One 

 part of diastase will convert into sugar 2000 

 parts of starch. Seeds which have germinated 

 always contain much more diastase than is 

 necessary for the conversion of their starch into 

 sugar. This excess of diastase Liebig thinks 

 can by no means be regarded as accidental. 

 One of the functions for which diastase ap- 

 pears to be created in the living seed to sub- 

 serve, is to contribute to the wants of the 

 young plant. "The starch in the seed," says 

 Johnston, " is the food of the future germ, pre- 

 pared and ready to minister to its wants when- 

 ever heat and moisture concur in awakening I 

 it to life. But starch is itself insoluble in | 

 water, and could not, therefore, accompany the i 

 ,406 



fluid sap when it begins to move and circulate. 

 For this reason diastase is formed at the point 

 where the germ first issues from the mass of' 

 food. There it transforms the starch, and ren- 

 ders it soluble, so that the young vessels can 

 take it up and convey it to the point of growth. 

 When the starch is exhausted, its functions 

 cease. It is then itself transformed and carried 

 into the general circulation. Or when, as in 

 the potato, much more starch is present than 

 is in many cases requisite, its function ceases 

 long before the whole of the starch disappears. 

 Its presence is necessary only until the leaves 

 and roots are fully formed, when the plant is 

 enabled to provide for itself, and becomes in- 

 dependent of the starch of the seed. When 

 this period arrives, therefore, the production of 

 diastase is no longer perceived. 



"This I have said is one of the purposes 

 which appears to be served by diastase in the 

 vegetable economy. That it is the only one 

 we have no reason to believe. There may be 

 others quite as interesting which we do not as 

 yet understand. This is rendered more pro- 

 bable by the fact that the diastase contained in 

 one pound of malted barley is capable of con- 

 verting into sugar five pounds of starch. 

 (Liebig.} It is the diastase in malt which dis- 

 solves the starch of the barley in the process 

 of brewing, but as the diastase contained in 

 malt is sufficient to dissolve so large a quan- 

 tity of starch, it is obviously a waste of labour 

 to malt the whole of the barley employed. One 

 of malt to three of barley would probably be 

 sufficient in most cases to obtain a wort con- 

 taining the whole of the starch in solution. 

 Advantage is taken of this property in the 

 manufacture of the white beer of Lou vain, and 

 of other places in Flanders, and in Germany, 

 where the light colour is secured by adding a 

 large quantity of flour to a decoction of a small 

 quantity of barley. And though at the tempera- 

 ture at which the seed germinates, more of this 

 substance may be necessary to transform the 

 same weight of starch than is required in our 

 hands, when aided by artificial heat, yet as 

 we never in the ordinary course of nature find 

 any thing superfluous or going to waste, there 

 is reason to believe that the diastase may be 

 intended also to contribute directly to the nou- 

 rishment and growth of the plant. As it con- 

 tains nitrogen, it must be derived from the 

 gluten or vegetable albumen of the seed ; and 

 as a young plant of wheat, when already 

 many inches from the ground, contains no 

 more nitrogen than was originally present in 

 the seed itself (Boussingault), this diastase 

 may only be the result of one of those trans- 

 formations of which gluten is susceptible, and 

 by which it is rendered soluble, and capable 

 of aiding in the production of those parts of 

 the substance of the growing plant into which 

 nitrogen enters as a necessary constituent." 

 (/. F. W. Johnston's Lectures.} 



DIBBLE (from dipfel, Dutch, a sharp point). 

 An instrument or conical stick to make holes 

 in the ground for setting grain, plants, &c. 

 "The subject of drilling by machinery," say 

 the Messrs. Ransome of Ipswich, "naturally 

 suggests the consideration of.whether the ope- 

 ration of dibbling may not be similarly accom- 



