CHEMICAL AND PHYSIOLOGICAL STUDIES. 171 



lithium, magnesium, ealeium, and at times silicon. Of these, the 



nitrates and nitrites of sodium and potassium, the phosphates and 

 chlorides of the same metals, and the salts of calcium and silicon, 

 occur in the sap of most plants, silica being present in the sap of cereals 

 to a considerable extent. In sea-weeds and shore-plants, iodides and 

 bromides of sodium and potassium are also found. Sulphates of the 

 above metals also occur. 



c. Dissolved Carbohydrates (sugars — \'iz., glucose, cane-sugar, 



and mannite, inulin), and amides (asparagin). Dextrins also occur 

 as intermediate products between starch and sugar ; gumS, such as 

 arabinose, tragaeanth, &c., may also be present. ProteidS, albumoSCS, 

 and peptones are also present at times. Sume of the proteids — e.g., 

 gluten — are insoluble. 



d. Soluble Alkaloids and GluCOSides.— These are bodies which 

 are intermediate products in the katabolism of nitrogenous substances 

 and protoplasm in plant-cells. The alkaloids are amides — viz., are 

 NH3, in which one or more H atoms are replaced by a radicle. The 

 glUCOSideS are nitrogenous bodies composed of amines combined with 

 glucose. Both of these bodies separate out sooner or later in the cell, 

 and are rendered harmless . 



Examples of the alkaloids are: quinine {Cinchona), nicotine fa liquid 

 alkaloid contained in the leaves of Kicolinna tahaca), atropine (in the 

 berries of Alropa helltidonna), strychnine (in the seeds of ,'<injrlnio.s nux 

 vomica) ; and, as instances of glucosides, may be given, digitoxiii ( Diijiln/i-i 

 jmrpunu), picrotoxin, and many others. In the case of the leaves of 

 Prunus Laurocerasus, a glucoside amygdalin is present, which, when 

 acted upon by emulsin (an enzyme), breaks up into hydrocyanic 

 acid, glucose, and benzoic aldehyde, this being one way in which the 

 glucosides are split up in plants (hydrolysis).* The glucosides may 

 be confotmded at times with tannin, with which substance glucose often 

 exists in loose combination. 



e. Ferments. — These are the unorganised ferments or enzymeS, such 

 as diastase, papain, and the peptic ferment in the leaf-cells of 

 Drosera. Tliey are ver}- important bodies. Diastase converts Starch 

 into dextrins (achroodextrin, erythrodextrin) and sugar (glucose), 

 and the peptic ferments convert the prOtcidS into albumoSCS and 

 peptones, bodies more suitable for assimilation than the proteids. [The 

 organised ferments belong to the Fungi, and one of the best known 

 is Saccharotnyces, the yeast-fungus.] Other ferments are invCFtase, 

 which inverts cane-sugar, cytase, lipase (a fat-splitting ferment), and 



synaptase. 



/. Organic Aeids.t — These may be present as acids, or in combination 

 with mineral or organic bases in the cell. The acids found may be 



oxalic, malic, citric, racemic, and tartaric. Tannic and gallic 



acids are often present, and salicylic acid is found in the cells of 

 GaitUheria procinahi-n^ as methyl-salicylate. The acids are in many 

 cases bye-products of cell-metabolism— viz., o.xalio acid. Calcium 



* Another such instance is where salicin is split up by means of 

 sj'naptase into saligenol and glucose. 



t Inorganic acids (viz., HNO3) may also be present at times, and NH3 

 (ammonia) may occasionally be found. In the latter case, however, amido- 

 acids are soon formed. 



