THE BIO-CHEMISTRY OF ANIMALS AND PLANTS 109 



acid potassium sulphate, whilst the crystallised glucoside from 

 Sinapis alba, called Sinalbin, gives rise to p-oxy-toluol — 

 mustard oil, and to the acid sulphate of the base sinapine, 

 besides dextrose. The base sinapine is easily hydrolysed into 

 choline and sinapic acid, and sinapic acid has been lately 

 synthesised by Graebe and Martz, after having been recognised 

 by Gadamer as a derivative of dimethyl-pyrogallic acid. 



It is questionable, however, whether all these substances 

 are merely excretory and final products of protein cleavage. 

 Their formation and presence may have quite a different 

 significance. Naegely has suggested that they are weapons of 

 defence against the attacks of bacteria. The enzymes which 

 give rise to prussic acid, benz-aldehyde, mustard oil, etc., are 

 only set free after injury to the cells which contain them, and 

 the substances liberated comprise some of the most active 

 antiseptics and bactericidal agents known. 



Phyto-toxins. — We are thus led in logical sequence to con- 

 sider next another class of substances, intimately related to 

 vegetable proteins, namely the phyto-toxins. These highly 

 poisonous substances occur preformed in plants, and are by 

 most observers regarded as proteins ; they give the protein 

 reactions ; they can be salted out of their solutions in definite 

 fractions, are precipitated by alcohol and destroyed by pro- 

 teolytic enzymes. Their protein nature has, however, been 

 questioned, and two other views have been advanced : one of 

 these is that the toxic principle is simply carried down mechani- 

 cally with the protein, whilst according to the other the toxic 

 principle is of the nature of an enzyme. 



Against the first of these views it may be urged that the first 

 fraction produced by salting out (the globulin), which usually 

 carries down all the impurities, does not contain the toxin ; 

 and against the second view, we have the fact that the phyto- 

 toxins produce their effect according to the law of definite 

 proportions, which is quite different from the laws which 

 regulate the catalytic action of enzymes. 



The best known phyto-toxins are the following : 

 1. Ricin. — This occurs in the seeds of the castor-oil plant 

 (Ricinus communis). It was first isolated by Stillmarck in Kobert's 

 laboratory. He considered it to be an albumose on account of 

 the way in which it could be salted out from solution, but his 

 substance was probably a mixture. Osborne, Mendel, and 



