YEAST-LIKE FUNGI OF HUMAN INTESTINAL TRACT 21 



5 of these along the entire puncture or they may be so close together that 

 the culture approaches the 2nd type of growth. Occasionally some cultures do 

 not develop these at all. For this reason several cultures were usually made 

 at one time. In other cases instead of the bushy growth appearing, there were 

 developed a number of root-like radiations resembling the secondary roots 

 arising from the tap root. To this group belong Oidium albicans, the sprue 

 organism, and 1 or 2 others which will be described. Plaut ('03b) figures a 

 typical growth of this kind. In the study of the white and golden types described, 

 52 cultures were tested in gelatin stabs. Of these 30 showed a villous growth, 

 while 22 were nodose or echinulate. In a study of 22 named cultural yeasts, 

 11 produced a villous growth while the same number did not. 



Sugar-Free Mediums. Aside from milk, the sugar-free mediums were used 

 as checks for the same type of mediums containing sugar. Pellicles, rings, 

 and grease films are produced in these mediums much as in the sugar-con- 

 taining ones. 



Pellicles, Rings, and Grease Films. A few characteristic cultural develop- 

 ments in liquid mediums need consideration at this point. A gray, dry pellicle 

 containing air is formed within 2 days in the case of the Mycoderma species. 

 This pellicle is characteristic and is easily distinguished from the type to be 

 described next. It resembles the pellicle produced by Bacillus subtilis in bouillon 

 culture. With some yeasts a gradual accumulation of cells on the surface 

 forms a thick, white layer which is moist and easily dislodged. This is usually 

 developed only after several days of growth, and if the tubes are disturbed at 

 intervals it does not appear. In the case of Oidium albicans and the sprue 

 organism this type of growth is present and very characteristic. 



With certain species a growth of cells takes place at the surface of the 

 medium where it is in contact with the glass. This soon results in a distinct 

 white ring which frequently becomes dislodged when the tube or flask is dis- 

 turbed and sinks to the bottom where it still retains its original form. This 

 ring is most distinctive at the end of 2 or 3 days, since species which do not 

 form a distinct ring often give this appearance in older cultures due to the 

 accumulation of cells as the liquid evaporates. 



By a grease film is meant a 'scum' which is thin and transparent. It 

 resembles a fine covering of oil in the surface and may be seen at the end of 

 a day or 2 only by holding the flask or tube in such a way as to allow the 

 light to reflect from the surface. Tilting the flask serves to render this more 

 distinct since the film remains attached to the glass and shows a distinct grayish 

 layer above the medium. In dextrin yeast water this scum approaches a 

 pellicle in consistency and can be clearly seen at the end of 3 or 4 days. 



Turbidity and sedimentation are not distinctive characters in the yeast cul- 

 tures, although some yeasts form a clear solution after a week of growth as 

 contrasted with the rather turbid condition in other cultures. 



Solid Mediums. Streak cultures on agar, carrots, and gelatin are useful 

 mainly in distinguishing yeasts of different colors or shades of color, and such 

 gross types of growth are those mentioned earlier. They are of limited value, 

 however, for the differentiation of species on account of the sudden and inex- 

 plicable variations which they undergo. All the pink yeasts studied retained 

 characteristic growths on agar and carrot slants under all conditions. 



Giant Colonies. The employment of giant colonies for specific differentia- 

 tion has been emphasized by Lindner ('05), Will, Geiger, and others. The 

 chief advantage of giant colonies lies in the ease with which they may be 

 photographed and thus serve as comparative charts. The method of developing 



