GLOSSARY. DENTINE DICOTYLEDONOUS. 593 



shows the same relation when the density of water is taken as 1. 

 Thus, if the body weigh in air 75 grains, and in water 60 grains, 

 then 75 60 or 15 : 75 :: 1 : 5 the body in this case being 

 found to be five times heavier than water. 



The specific gravity of gaseous bodies is usually taken in refer- 

 ence to atmospheric air as a standard ; sometimes, also, in reference 

 to hydrogen, the lightest known body. It is plain that if a flask 

 capable of containing any definite measure, such as a hundred 

 cubic inches, of air, be weighed carefully when filled with different 

 gases, the relative densities of each will be discovered. 



The hydrometer is a convenient instrument for ascertaining the 

 density of liquids. It is a tubular instrument, closed at both ends, 

 and being loaded, for example, with mercury at the lower part, 

 floats upright, while the very slender upper part, of perfectly 

 uniform diameter, rises above the surface of the fluid in which it 

 is immersed. When put into water, it sinks to the beginning of 

 an ascending and descending scale. When put into a heavier 

 fluid, it rises so many degrees in proportion as that fluid is heavier 

 than water. If put into a fluid lighter than water, it sinks so that 

 an ascending scale shows how many degrees that fluid is lighter 

 than water. The instrument is delicate in proportion as that part 

 of the stem to which the scale is attached is more slender and 

 uniform in diameter throughout. 



DENTINE. The substance that forms the body of a tooth, more or less 

 allied to bony substance. 



DERMA. The true skin, cutis vera, or coritim often incorrectly 

 termed dermis : epidermis, for cuticle or scarf-skin, is correct ; but 

 there is no such word as dermis. 



DERMATODECTES. See Parasite. 



DEXTRINE. The same as British gum obtained from starch by heat, 

 or by heat and sulphuric acid. See p. 329. 



DIAPHRAGM. The midriff, or muscular partition between the chest 

 and abdomen. 



DIARRHCEA. Looseness of the bowels. It is sometimes produced 

 by certain kinds of food. Thus young green turnip-leaves, in 

 the beginning of winter, often bring both cattle and sheep severely 

 down from their condition acquired at grass ; even on cows, while 

 such food augments the yield of milk, it is apt to produce severe 

 looseness. Potatoes often produce scouring in cattle till they have 

 become accustomed to this kind of food. Horses are never so 

 affected by potatoes, and potatoes are not given to sheep. 



DIASTALTIC. Applied to the reflex system of nerves, their effect being 

 produced through the spinal marrow. 



DIASTOLE. Opposed to systole ; diastole signifying the dilatation of 

 a cavity of the heart, or of an artery. See Systole. 



DICOTYLEDONOUS. Applied to the great division of plants in which 



