PRO 



PRO 



with the leaves on, and in a living 

 state. A few plants ar(> propajjateil 

 by ('iittin<rs of the leaves, the petiole 

 of the leaf being sliijped ofl'froin the 

 parent plant, and probably containing 

 the latent embryos of buds. Graft- 

 ing and budding are processes which 

 have been already explained. In- 

 arching may be described as a spe- 

 cies of grafting, in which the scion is 

 not separated from the [)arent plant till 

 it has become united with the stock." 



PROPEDS. The same as proiegs. 



PROPHYLACTIC. Preventing 

 disease. 



PROPORTIONS, CHEMICAL. 

 See Equivalents and Atom. 



PROSENCHYMA. Elongated cel- 

 lular tissue, as that of woody struc- 

 ttues. 



PROTEIN. The pure basis of the 

 animal principles : it is separated 

 from albumen, or fibrin, by dissolving 

 them in caustic potash, and precipita- 

 ting by acetic acid. It is gelatinous, 

 gray ; when dry, semitransparent, 

 and insoluble. Its composition is C 

 55-7 . H 6-8 . N IGI . O 21 2 ; formu- 

 la (Mulder) C40 Hu N3 O,. (Liebig 

 construes the composition into C+^ 

 Na H36 Oh) ; symbol Pr. It is a body 

 of great interest, since in its combi- 

 nations with sulphur, phosphorus, 

 ammonia, &c., most animal tissues 

 are formed. Thus 10 Pr. -\- sulphur, 

 i phosphorus, is albumen. 10 Pr.,2 

 sulphur, \ phosphorus, is another form 

 of albumen. 



PROTOTHORAX. The first seg- 

 ment of the thorax in insects. 



PROTO-SALTS. Oxides ; com- 

 pounds, the bases of which are com- 

 bined with but one equivalent of ox- 

 ygen. 



PROTOZOA. The lowest animal- 

 cules. 



PROTRACTOR. " A mathemat- 

 ical instrument for laying down an- 

 gles on paper, used in surveying, 

 plotting, &.C. 



" In its simplest form, the protract- 

 or consists merely of a semicircular 

 limb of metal divided into 180 % and 

 subtended by a diameter, in the mid- 

 dle of which is a notch to mark the 

 position of the centre. On placing 



[ this notch over the angular point, and 

 laying the diameter along a given 

 straight line, an angle of any number 

 of degrees may be made by marking 

 the point on the paper which coin- 

 cides with the given degree on the 

 limb, and joining this point with the 

 centre when the instrument is re- 

 moved. The protractor is rendered 



i more commodious by transferring the 

 divisions to the edge of a parallel ruler. 

 " M'hen a survey is to be plotted 

 on a large scale, and it becomes ne- 

 cessary, in consequence, to lay down 

 the angles with consideral)le precis- 

 ion, a more complex apparatus is re- 

 quired. The most approved form of 

 the protractor may be described as 

 follows : It consists of an entire cir- 

 cle, connected with its centre by four 

 radial bars. The centre of the metal 

 is removed, and a circular disk of 

 glass fixed in its place, on which are 

 drawn two lines crossing each other 

 at right angles, the point of intersec- 

 tion denoting the centre of the pro- 

 tractor. Round the centre, and con- 

 centric with the circle, is fitted a col- 

 lar carrying two arms, one of which 

 has a vernier at its extremity adapt- 

 ed to the divided circle ; and the oth- 

 er a milled head, which turns a pin- 

 ion working in a toothed rack round 

 the exterior edge of the instrument. 

 The rack and pinion give motion to 

 the arms, which can thus be turned 

 quite round the circle, and set the 

 vernier to any angle that may be re- 

 quired. Each of the two arms is pro- 

 longed beyond the edge of the pro- 

 tractor, and carries a fine steel prick- 

 er, which is pressed down when the 

 instrument is placed in its required 

 position, and makes a small ptmcture 

 in the paper. It is essential that the 

 points of the two prickers and the 

 centre of the instrument be accu- 

 rately in the same straight line." — 

 {Sinnns on Mathematical Instruments.) 

 PROTUSILE. Capable of being 

 protruded and withdrawn. 



PROVENDER. Dry food. See 

 Fodders. 



PROXIMATE ANALYSIS. The 

 separation of a compound organic 

 body into its several complex parts, 



643 



