214 Report ok the Department op Bacteriology of the 



per ct. asparaginate (see column three) was first compared with two 

 modified formulae containing 0.2 per ct. and 0.5 per ct. of asparaginate 

 respectively (see columns one and two). As each of these formulae 

 was used in only two tests no definite conclusions can be drawn; 

 but it is evident that there is no distinct advantage to be gained 

 by using these larger quantities of asparaginate. A much longer 

 series of tests was made of a medium containing only 0.05 per ct. 

 asparaginate (see the fourth column). In ten of the sixteen cases 

 the counts obtained with 0.05 per ct. asparaginate are higher than 

 those obtained with 0.1 per ct.; while 0.1 per ct. of asparaginate 

 has allowed better counts only in five cases. The slight superiority 

 of the medium with the smaller amount of asparaginate may have 

 been merely accidental; but it is quite plain that as good results 

 can be obtained with 0.05 per ct. as with larger amounts. As the 

 asparaginate is the most expensive constituent of the medium, 

 perhaps it would be well in routine work to use 0.05 per ct. instead 

 of 0.01 per ct. (as given in Table I). The results are less satisfactory, 

 however, when the asparaginate has been lowered beneath this point. 

 In the fifth column five counts on a medium containing only 0.02 

 per ct. sodium asparaginate are given, and in the sixth column 

 four counts on a medium with the asparaginate omitted entirely. 

 All these counts except one (test No. 24 with 0.02 per ct. asparagi- 

 nate) were lower than the corresponding counts when 0.1 per ct. of 

 asparaginate was used, but the differences were never very great. 

 The greatest disadvantage of these two media cannot be shown by 

 figures. Colonies developed very slowly upon them and remained 

 small and undifferentiated in appearance. Although it is noi 

 absolutely necessary for a medium intended for quantitative work 

 to show differences in appearance between the colonies of different 

 kinds of bacteria, it is, nevertheless, a desirable feature if it can be 

 obtained without sacrificing either of the other two more necessary 

 qualifications. For this reason it is not advisable to use less than 

 0.05 per ct. of sodium asparaginate, even though it may be entirely 

 omitted without greatly affecting the count. 



A second series of tests, showing the effect of varying the dex- 

 trose content, is given in Table V. The six counts given in the 

 first two columns indicate an inferiority when as much as 0.5 per ct. 

 of dextrose is used, but the tests are too few in number to establish 

 the fact. More work on this point is to be desired. It would be 

 advantageous to use larger amounts of dextrose if it could be done 

 without lowering the count, because this sugar is of considerable 

 value in bringing out distinctions between the colonies of different 

 kinds of bacteria. The counts given in the fourth column of this 

 table would seem to show that reducing the dextrose content to 

 0.05 per ct. has lessened the number of colonies which develop; but 



