GROUP XXII  . Saponin.—Saponin and many allied bodies form an abundant soapy-looking froth when shaken up with water, and they are contained in a very large number of plants, the chief of which are the Quillaia saponaria, Polygala senega, sarsaparilla, and others, known collectively as soapworts . They all act as local irritants in the alimentary canal, and after absorption are more or less depressing to the muscular and nervous systems . They produce slight nausea and increased secretion of mucus . GRouP XXIII . Cyanogen.—This includes compounds of cyanogen such as hydrocyanic (prussic) acid, cyanides of potassium, sodium . &c., cherry-laurel water, amygdalin, bitter almonds and other chemical and vegetable substances which readily yield hydro-cyanic acid . Hydrocyanic acid is a general protoplasmic poison, all the lower organisms being very susceptible to its action, while in the higher animals it speedily depresses or paralyses all forms of nerve tissue . It enters into combination with haemoglobin, forming a bright scarlet compound and interfering with respiration . It kills by its paralysing effect on the motor ganglia of the heart and on the respiratory centre . Ggour XXIV . Ferments.—These include such bodies as pepsin, diastase, the pancreatic ferments, papain, the pine-apple ferment, taka-diastase and others, and serve to convert starch into saccharine substances, or albumen into peptone and albumoses .