174 CHARACTERIZATION AND IDENTIFICATION 



Giant Colonies 



Lindner l has devised another method which yields very good dif- 

 ferential characteristics. This involves the growth of giant colonies 

 which are much utilized today by bacteriologists and mycologists. 



They are made by inoculating 

 a large surface of gelatin at a 

 single point. The giant colo- 

 nies grow steadily until they 

 have reached larger propor- 

 tions than the ordinary colony. 

 The inoculation is accom- 

 plished by placing a drop of 

 dilution in the middle of a 

 large surface. At laboratory 

 temperatures (20 C.) it will 

 require two months for the 

 colony to reach its large pro- 

 portions. There is an 

 optimum temperature for each 

 variety which permits the 

 most characteristic form. 

 Giant colonies, in each case, 

 give a very different appear- 

 ance. (Fig. 72.) However in 



Fig. 72. Appearance of Giant Colonies of 

 Various Yeasts. 



1, S. Pastorianus; 2, S. mtermedius; 3, S. ellipsoideus ; 

 4, S. turbidans; 5, S. validus (after Lindner). 



most cases they merely 

 furnish characteristics of the 

 group and not specific 

 characteristics. Giant 

 colonies are sometimes susceptible to variations. 



The types of the cells in the mediums also furnish valuable in- 

 formation. Saccharomyces Ludwigii, S. marxianus, carlsbergensis 

 and P. membranaefaciens form mycelial filaments. Saccharomyces 

 Bailii produce ameboid cells (Fig. 31). 



Biochemical Activity of Yeasts 



The action of the yeasts towards the different sugars is valuable 

 information in their differentiation. The method of Lindner, 2 outlined 

 above, may be used. It should be determined whether the yeast de- 



1 Lindner, P. Das Wachstum der Hefen auf festen Nahrboden, Wochenschr. 

 Brau. 10, 1893. 



2 Lindner, P. Garversuche auf vershiedenen Hefen und Zuckerarten. Wochen- 

 sch. Brau. No. 17, 1900. 



