DIF 



DIG 



bour soon pays for the machine. A 



number of these wheels drawn by a 

 horse has been recently introduced. 



DICHOTO.MOUS (from Jff, twice, 

 and TEfivu, I cut). Bifurcate. It is 

 used in natural history to indicate 

 a division into two parts, especially 

 when it is repeated several times, as 

 in some stems. 



DICHROISM (from 6ig, and jpw/xa, 

 colour). Bodies which exhibit two col- 

 ours, as they are examined by reflect- 

 ed 01 refracted light. Dichromatic 

 is a derivative 



DICOTYLEbONS (from 6ic, and 

 KOTv?.iiduv, a seed lobe). One of the 

 great divisions of the vegetable king- 

 dom, including most plants and trees 

 of temperate climates. Tliey bear 

 seed with two lobes, like the bean, 

 have leaves freely veined, and the 

 trees grow with a conical trunk. The 

 term is synonymous with cxogens. 



DIDELPH YS (from di^, and dcAovr, 

 womb). A genus of animals resem- 

 bling the opossum and kangaroo, 

 which bring forth minute young, and 

 afterward nourish them in an exter- 

 nal pouch. Marsupials. 



DIDl'XAMOUS (from Sir, and ih- 

 va/iig, power). Flowers with four sta- 

 mens, two being longer than the rest. 

 See Botany. 



DIETETICS (from Siairaeiv, to 

 nourish). The study of varieties of 

 food. See Fodder. 



DIFFERENTIAL THERMOME- 

 TER. A thermometer with two 

 bulbs, invented to measure differ- 

 ences in temperature, but seldom 

 used. 



DIFFRACTION. See Deflection. 



DIFFUSION OF GASES. Pene- 

 tration of gases. The expression of 

 a phenomenon which occurs when 

 one gas is set free into another. 

 They mutually expand or diffuse into 

 one another, so as to produce, in time, 

 an equal mixture. The rapidity of 

 diffusion differs with different gases. 

 By reason of this law, noxious va- 

 pours rising from the earth are pres- 

 ently diluted into the atmosphere. 

 The composition of the air is the re- 

 sult of the diffusion or admixture of 

 the several gases it contains. This 



U 



passage takes place through all po- 

 rous vessels, tissues, &c. In virtue 

 of this property, gases are said to act 

 as a vacuum towards each other. 



DIFFUSUS. Spreading: used in 

 botany. 



DIGESTER. A strong iron or 

 copper pot, the lid of which tits steam- 

 tight, and either screws on or is press- 

 ed by clamps, and is furnished with a 

 safet)'-valve. It is used for boiling or 

 digesting substances at a heat great- 

 er than boiling water, and is especial- 

 ly useful for extracting jelly and glue 

 from bones, skins, horns, &c. 



DIGESTION. In physiology, the 

 change through which food passes in 

 the stomach for the production of 

 chyme. Food received into the stom- 

 ach is speedily attacked by a peculiar 

 fluid therein, the gastric, which has 

 the power of rendering soluble the in- 

 soluble parts : this it effects by pro- 

 ducing a change nearly resembling 

 fermentation. The gastric juice is a 

 portion of the membrane of the stom- 

 ach in a peculiar state of change, re- 

 sembling diastase, and supposed to 

 owe its power to a principle called 

 pcpsii}, but being in reality active only 

 because in a state of change. The 

 food acted on by this agency is con- 

 verted into a pasty mass called chyme ; 

 this, passing into the bowels, is sep- 

 arated into a fluid part, chyle, which 

 is absorbed by the veins and absor- 

 bents of the intestines, and reaches 

 the blood to add to that fluid. There 

 is reason to believe that starchy and 

 saccharine bodies are converted into 

 lactic acid, and in part into oils, by 

 digestion. The remaining thickened 

 chyme, receiving several excretions, 

 becomes mere feculent matter. The 

 process of digestion requires from one 

 to four hours, according to the food. 

 Raw substances are digested more 

 rapidly than boiled, fresh than salt. 

 It is best conducted when the body 

 and mind are in a state of rest. 



DIGESTION IN CHE.MISTRY. 



The exposure for a long time of any 



substance to the action of water or 



a solvent at a gentle heat. 



DIGGING. See Spade. 



DIGITALIS. The generic name 



22a 



