ii6 MORPHOLOGY AND LIFE-HISTORY OF YEASTS. 



ends, and in some species slightly constricted in one or two 

 places. Cells of this kind were noticed by Pasteur (XII.) during 

 his researches on wine. They were also found by Reess (I.) in 

 the secondary fermentation of certain wines examined by him ; 

 and this worker named them Saccli. Pastorianus in honour of 

 the French scientist. Cells of this type have been more fre- 

 quently observed by subsequent investigators, and this specific 

 name has been gradually modified into a morphological term. 

 When it is said of a yeast that it exhibits pastorianus forms, or 

 is of the Pastorianus type, the term merely implies that under 

 normal conditions the sedimental yeast of the species in question 

 chiefly forms cells that are sausage-shaped, and not globular, 

 oval, or elliptical. An example of this kind is afforded by 

 Saccli. Pagiorianus /., illustrated in Fig. 129. This species was 

 discovered by Haxsen (II. and XII.), in 1880 and 1881, in the 

 air at the Alt-Carlsberg brewery, Copenhagen, and was intro- 

 duced into the literature, under the above name, by him in 

 1882, after he had succeeded in proving that it had also crept 

 into the stock yeast of this brewery, imparting to the resulting 

 beer an obnoxious bitter by-flavour and a smoky smell. It is 

 therefore a virulent pathogenic yeast (in the technical sense). 



It would be a great mistake on the part of the reader to 

 assume, from the foregoing sketch of the three main typical 

 foi'ms of yeast cells, that each species of yeast invariably assumes 

 the same form. This is not the case, a powerful influence on 

 the form being exerted by the conditions of cultivation. This 

 last fact was unknown, and indeed undiscoverable by the 

 methods in use, at the time Reess set up his specific classifica- 

 tion based solely on the form of the cells. Thus, up to the year 

 1882, it was thought that the bottom-fermentation yeast used 

 in brewing always consisted of the one single species Sacch. 

 cereviske ; and it was not until 1883 that E. Chr. Haxsex (XII.) 

 showed that we have to I'eckon with a lax-ge number of species, 

 and that consequently the names Sacch. cerevisice, Sacch. Pas- 

 torianus, Sacch. elHjJsoideus, &c., could hencefoith be merely used 

 as group names. Since that time, no small portion of this 

 worker's investigations has been devoted to the question of the 

 dependence of cell form on the conditions of cultivation, and to 

 the elucidation of the fact that, morphologically, the character 

 of a species of yeast does not reside in the form of the cell alone, 

 but also in the manner of its dependence on the external con- 

 ditions of which it is the result. If these conditions be known 

 to a certain extent, then the foi'm of the cells constitutes a very 

 valuable and fairly reliable indication. Since, like other mani- 

 festations of vitality, the form of the cells is a I'esultant of two 

 components, namely, inherited properties and the sum of all the 

 external influences, it is evident that, even if the unifoi'mity 

 of the latter conditions could be made absolutely certain, the 



