xii CONTENTS 



PAGE 



Properties 268 



Reactions 268 



Isolation . 269 



Origin of alkaloids in the plant 271 



Ptomaines 273 



Purine bases ... . . " . . . . . . 276 



Physiological significance of nitrogen bases . . 280 



SECTION VIII. THE COLLOIDAL STATE 283 



Suspensoids 287 



General properties 287 



Optical properties 287 



Electrical properties 288 



Protective action 291 



Emulsoids 292 



General properties 293 



Gel formation 299 



General properties of gels ... .... 300 



Nature of gels ... 301 



Adsorption ............ 302 



Enzyme action of colloids ... - , . 306 



SECTION IX. PROTEINS . 310 



General properties . . 311 



Microchemical reactions . . . . . . .3*7 



Proteins as colloids ... . . . . . . .317 



Amphoteric electrolytes 320 



Decomposition products . . 322 



Amino acids obtained as cleavage products of proteins . . 324 



Polypeptides ... 328 



Occurrence of airn'no acids in plants , . ... 330 



Classification of proteins . . . 331 



Comparison between vegetable and animal proteins .... 337 



Extraction of proteins 339 



Synthesis of amino acids in the plant . * .... 342 



SECTION X. ENZYMES . ... . . . . .346 



Classification . . . 350 



Isolation . . ..; ^ . 351 



Chemical constitution . . 351 



Properties . . . . 352 



Colloidal nature of enzymes . " . . . . . . . 353 



Mode of action . . . 354 



Activators . . . y 35^ 



Paralysers . . . . .* .358 



Anti-enzymes . . . .- 360 



Enzymes and the laws of mass action 363 



Consideration of certain types of enzymes . . . . . 367 



Lipase ...... s 368 



Isolation . 369 



Quantitative determination of activity 370 



Diastase . . . . . . . , . . 370 



Isolation , 371; 



Quantitative determination of activity . . , . 372 



