20 HARRY WARREN ANDERSON 



uninoculated. Another set of yeast water alone was inoculated with the same 

 organisms. One series was kept at 35-36 C. and another at 25-27 C. Before 

 recording the results with any yeasts several trials were made in order to 

 eliminate chance variation. 



The variations in fermentation of sugars recorded by Ashford in the case 

 of his sprue organism were not met with when vigorous young cultures were 

 used. On several occasions when cultures of different ages were taken at 

 random variation was noted. The cause of this variation was not determined, 

 but there is no doubt but that it does occur and should be guarded against. 



Litmus Milk. This medium is useful for separating the yeasts into 3 dis- 

 tinct groups: (1) those which render the milk more alkaline, (2) those which 

 produce no marked change, and (3) those which produce acidity. No yeast 

 studied coagulated milk within 2 weeks, and very few produced acidity. Prac- 

 tically all the forms isolated from feces belonged to the first 2 groups. By 

 acidifying the litmus until it has a strong violet color the change to the alkaline 

 condition is very marked. The tubes were incubated at 25-27 C. and 35-36 G. 

 and were observed at frequent intervals. 



Gelatin Mediums. Gelatin-stab cultures are especially useful in determining 

 whether or not the yeast studied produces elongated cells. Yeast water, beer- 

 wort, and nutrient broth gelatins were most commonly employed. The beerwort 

 gelatin is most satisfactory for growing giant colonies since it is easily pre- 

 pared. The stab cultures are most satisfactorily observed in yeast-water gelatin 

 since gas-forming yeast produce bubbles in beerwort gelatin and break up the 

 mediums. The type of growth in gelatin depends to a certain extent on the 

 consistency of the medium and care should be taken to secure a firm gelatin. 



A few of the yeasts studied liquefied gelatin while the great majority did 

 not. There was a decided variation in several species which were at one time 

 liquefying, at another not. Such variations may account for the difference in 

 the description given of Oidium albicans by several authors. Frequently old 

 cultures were found to begin liquefaction after they were left several weeks 

 undisturbed. Such liquefaction is probably not due to the activity of the living 

 cells, and should not be regarded as what is ordinarily spoken of as liquefaction. 



Three general types of growth in gelatin are observed among the white, 

 nonliquefying group. In the 1st type there is a more or less uniform, straight, 

 white line following the needle puncture. This is filiform at first but may later 

 become decidedly nodose. Practically all yeasts take this form during the first 

 few days, and then pass over into 1 of the 2 types to be described. The 

 2nd type has a villous form of growth. Within this type there is a wide 

 variation from forms with individual filaments extending outward at right 

 angles from the axis, like the bristles on a brush, to those having branched 

 bushy filaments. The villous condition may develop early, as in certain Myco- 

 derma types, or it may not appear until the culture is a week old. The dense- 

 ness of the radiating hyphae, their length, and degree of branching is usually 

 characteristic. Under the hand lens these radiating threads often appear monili- 

 form due to the groups of buds at the ends of the cells of the hyphae. The 

 3rd type is really a modification of the 2nd, but on account of its importance 

 in distinguishing forms of the Oidium albicans type, it is described separately. 

 At first the growth is filiform ; later it becomes somewhat nodose. In about 

 5 or 6 days after inoculation there appear, radiating hyphal elements near the 

 surface of the medium. These may extend to a depth of one-half inch below 

 the surface or may not appear at all. Later from scattered points along the 

 nodose line, fine, individual, bushy growths appear. There may be only 4 or 



