YEAST-LIKE FUNGI OF HUMAN INTESTINAL TRACT 25 



PRODUCTION OF ACIDITY AND ALKALINITY IN LIQUID MEDIUMS 



Table 4 gives the results of the titrations of cultures in several carbohydrate 

 mediums. These results represent the total acidity or alkalinity at the end of 

 the period indicated in the table. The tests, as here recorded, are intended 

 mainly to indicate whether the organism concerned renders the medium decidedly 

 alkaline or acid after a period of growth. 



It is unfortunate that those who have used the reactions with carbohydrate 

 mediums for specific separation in the yeasts have not used more care in 

 recording their results. Usually the descriptions of the methods employed are 

 entirely lacking and the results are recorded in a table as positive or nega- 

 tive, without indicating the length of time after inoculation when the tests were 

 made or the total amount of acid produced. The basic substance employed 

 in making the carbohydrate mediums and the initial acidity are not given in 

 most cases. 



Will and Geiger have been more careful in this respect and their results 

 show that the time at which the titrations are made is very important. It is 

 strange that Castellani should find acid developed in most of his carbohydrate 

 mediums with a large number of his Monilia species while a decided alkaline 

 reaction in milk is recorded for these same species. 



In order to make a more careful study of the changes in acidity during 

 the first month of growth in liquid mediums, 6 of the 20 organisms selected 

 were grown in flasks of yeast water alone and also with the carbohydrates 

 added. These were tested at 3 periods, as indicated in Table 5. 



The original acidity of the yeast water was near + 1 to phenolphthalein. 

 Uninoculated flasks were always incubated with the others and titrated at 

 the ends of the periods as in the case of the inoculated ones. This precaution 

 was used in order to show that the little evaporation which occurred did not 

 have a decided effect on the results, and to give a large number of check 

 titrations of the original mediums. The titrations were made against n/20 

 NaOH using phenolphthalein as an indicator. The results are expressed in 

 the number of cubic centimeters of n/10 NaOH it would require to neutralize 

 the acid produced in 100 c.c. of the medium. If the acidity decreased instead 

 of increased it is expressed by a negative sign; in other words, it would take 

 this amount of n/10 HC1 to neutralize the alkali in 100 c.c. of the medium. 

 Five c.c. portions were withdrawn by means of sterile pipettes,, and the average 

 of 2 titrations was taken in all cases except at the end of the final period, 

 when 3 titrations were made from each flask. 



Discussion of Results. The results given in Tables 4, 5, and 6 are 

 evidence that the reactions brought about by the intestinal yeasts are 

 variable, not only among different species but in the same species 

 with different carbohydrates. It is also evident that titrations made 

 at different times during the course of the growth show variations in 

 the same species. The temperature at which the cultures are kept 

 also has an influence on the degree of acidity. That the change in 

 acidity is not due primarily to the carbohydrate present is evidenced 

 by the fact that yeast water without the addition of carbohydrates 

 gave similar results to the yeast water carbohydrate mediums. The 

 addition of certain carbohydrates tend, however, to vary the degree 



