YEAST. 



[ 693 ] 



ZOOPHYTES. 



a time, the growth slackened, finally no fur- 

 ther increase took place, undoubtedly be- 

 cause all was removed from the hquid which 

 could serve for their growth. Gromng glo- 

 bules from this experiment are figured in 

 PI. 20. fig. 23. 



By the obseiTations of numerous compe- 

 tent investigators, it seems certain that the 

 fermentation of beer, of wine, and in fact all 

 vinous fermentation, is efi^ected by the growth 

 of this plant ; and after the evidence brought 

 forward in the articles Fermentation, 

 ToRULA, and Vinegar Plant, there is 

 little doubt that the Vinegar plant, the 

 Oidium lactis, and other supposed distinct 

 plants, are but forms of the Yeast-plant. 

 Fig. 24 (Pl. 20) exhibits the condition of 

 the Yeast- plant on the surface of exhausted 

 wort of malt, before the Vinegar-fungus 

 appears ; fig. 761, page 646, the Torula-iona 

 at the margins of the surface of liquids. 



We cannot clearly make out any difi^erence 

 between the 'top-yeast' and 'bottom-yeast' 

 (ober-hefe and unter-hefe of the Germans). 

 AVe do not believe the yeast-cells ever bm-st 

 to discharge reproductive granules. The 

 globular form is known by various names, 

 as Mycoderma cerevisice, Desm., which 

 agrees with Cryptococcus glutinis, Kiitz. ; 

 the globular form in the Vinegar-plant is 

 Kiitzing's Ulvina aceti ; the filamentous 

 form with simple moniliform fruit (fig. 761) 

 is Torula cerevisice, Turpin ; without fruit, 

 species of Hygrocrocis or Leptomitus ; the 

 final form being apparently Penicillium ylau- 

 cum. 



It is needless to repeat here the details 

 given under Fermentation, but it may be 

 added here that Turpin imagined that yeast 

 was formed by metamorphosis of the starch- 

 granules or similar bodies of vegetable cells; 

 and Schleiden seems to believe still (what 

 Kiitzing, Reissek, and others decidedly as- 

 sert) that the globular cells, the earliest 

 condition of yeast, quickly appearing in all 

 saccharine vegetable juices, or solutions 

 containing sugar and albuminous matters, 

 are 'autochthonous,' or rather pseudo-organ- 

 isms, formed by the abnormal and extra- 

 ordinary development of organic matters 

 separated fi-om their natural position, and 

 capable of advancing only to a certain degree 

 of this false or diseased organization, when 

 they perish. These views are scarcely worth 

 notice after the numerous experiments which 

 have proved that no such phaenomena occur 

 when the germs of these certainly definitely 

 organized species of plants ai*e carefully 



excluded. The Yeast-plant is truly most 

 ubiquitous, but so are the conditions for its 

 growth, while its reproductive power is enor- 

 mous, and its small size renders it liable to 

 be scattered by imperceptible movements of 

 the air. Aspergillus glaucus is almost as 

 constant in its favourite nidus, cheese ; 

 Mucor mucedo on paste, &c. ; Botrytis vul- 

 garis on dead leaves and stems in damp 

 places, &c., and all these are certainly no 

 pseudo-morphic productions ; and if, as we 

 believe, yeast is but the conidial form of 

 Penicillium glaucum, there has been no lack 

 of the spores of the latter in the air, in any 

 situation where we have ever exposed vege- 

 table substances for any length of time to a 

 damp atmosphere. 



BiBL. Turpin, Mem. de VInstitut, xvii. 

 p. 93 (1840); Schleiden, Grundziige der 

 Botanik, 3rded. i. p. 235 {Principles, p. 32); 

 and the Bibl. of Fermentation. 



YEW. See Taxus. 



Z. 



ZAMIA, Lindl. See Cycadace^. 



ZETES, Koch. — A genus of Arachnida, 

 of the order Acarina, and family Oribatea. 

 It is consolidated with Galumna. 



ZINC. — The crystals of the lactate, as 

 deposited from an aqueous solution, are re- 

 presented in PI. 7- fig. 20 ; they belong to 

 the right rhombic prismatic system. 



The chloride of zinc is useful as a preser- 

 vative of animal tissues. (See Preserva- 

 tion, p. 535.) 



Bibl. That of Chemistry. 



ZONARIA, Harvey {Aglaozonia, Zanard, 

 Kiitz.). — A genus of Dictyotacese (Fucoid 

 Algse), of which the British species, Z. par- 

 vula, forms olive-green, membranous, fan- 

 shaped fronds, 1 " or more in diameter, grow- 

 ing over stones or corallines, to which it 

 attaches itself by whitish fibres on the lower 

 surface. It is scarcely marked with con- 

 centric lines like Padina. The fructification 

 occurs in scattered sori on both surfaces, 

 and is apparently analogous to that of Pa- 

 dina, but requires further examination, 

 since Thuret has shown that the true Dicty- 

 otacese have peculiar reproductive organs, 

 spores, tetraspores, and antheridia, so that 

 they stand between the Fucacese and the 

 Floridese. 



Bibl. Harvey, Brit. Mar.Alg. p. 38. pl. 

 6D.; Thuret, Ann. des Sc. nat. 4 ser. iii. 

 p. 25. 



ZOOPHYTES. See Polypi. 



