ORGANIC STIMULANTS AND POISONS. 247 



observed the contrary. Further attention should be devoted to 

 Hayduck's observation that the amount of nitrogen compounds 

 absorbed by yeast from wort increases with the quantity of hops 

 employed, bearing in mind a statement made in this connection 

 by BEHRENS (VIII.). With regard to the part played by hop 

 resins in the formation of " head " on the fermenting wort, com- 

 pare p. 183, vol. ii. 



Many yeasts are rather sensitive to the tannins in wine must 

 and certain fruit musts, as was observed by A. ROSENSTIEHL (I.). 

 This is a well-known fact among vintagers, and special measures 

 are adopted in consequence. 



The nature of the resins and ethereal oils rendering the fer- 

 mentation of juniper-berry juice a difficult operation is still 

 unknown. G. KASSNER (I.) published a note on this point. 



According to WERNKE (I.), oil of mustard (C 3 H 5 .NCS) in the 

 proportion of i : 16,700 is fatal to yeast. 



The maltol (C 6 H 6 3 ) first discovered by J. BRAND (III.) in 

 caramel-colour malt, and regarded by KILIANI and BAZLEN (I.) as 

 a methylpyromeconic acid, is stated by H. WILL (XXVI.) to have 

 but a feeble toxic effect on yeast and to be devoid of influence in 

 practice, for though o. i per cent, will delay yeast reproduction, 

 the amount present in wort is far below that proportion. Even 

 the furfural (C 5 H 4 2 ) produced during the curing of malt (see p. 207, 

 vol. ii.),from which it passes into the wort though rarely found 

 in beer is stated by H. WILL (XXVII.) to have but little effect 

 on yeast, though the different yeasts are variously affected and all 

 are killed by an addition of 0.5 per cent. It has not yet been 

 definitely settled whether and to what extent this or other pro- 

 ducts of the curing of malt are responsible for the admitted fact 

 that dark worts furnish a lower attenuation than those from pale 

 malts. Researches on this point were undertaken by M. IRMISCH 

 (I.) and F. Niemeyer. 



Among the compounds of the aromatic series, WERNKE (I.) 

 states that benzene (C 6 H 6 ), toluene (C 6 H 5 .CH 3 ), and xylene 

 (C 6 H 4 (CH 3 ),) are fatal to yeast in the proportions of i : 200, 

 i : 300, and i : 800 respectively. The action of carbolic acid or 

 phenol (C 6 H 5 .OH) on yeasts was studied by Lemaire, W. BUCHOLZ 

 (I.), H. HOFFMANN (V.), and H. FLECK (I.), and afterwards more 

 carefully by C. KNOESEL (I.), who found that an addition of about 

 0.5 per cent, of phenol, at room temperature, kills the cells. 

 According to BIERNACKI (I.) the introduction of a second and 

 third hydroxyl group into phenol lowers its toxic properties, so 

 that resorcin (C 6 H 4 .(OH) 2 ) is only half as powerful, and pyrogallol 

 (C 6 H 3 (OH) 3 ) has only one-third the strength of phenol. K. YABE 

 (V.) confirmed this observation, and found it also applicable to 

 pyrocatechin, hydrokinone, and phloroglucin. Benzoic acid, even 

 in the small proportions in which it is soluble in aqueous liquids, 

 has a somewhat powerful effect on yeasts, according to the dis- 



