104 Report of the Department of Bacteriology of the 



A DISCUSSION OF THE ADVANTAGES AND DISADVAN- 

 TAGES OF THE MICROSCOPIC AND PLATE COUNTS. 



The advantages and disadvantages of these two methods have been 

 tabulated in Table XI and a brief discussion of the more important 

 points follows. 



Table XI. — The Advantages and Disadvantages of the Direct Microscopic 

 Method as Compared with the Plate Method. 



disadvantages. 



Direct microscopic method. 



Plate method. 



1. Difficult to measure so small a quan- 



tity of milk accurately. 



2. The sample measured is too small to 



be representative. 



3. Dead bacteria may be counted. 



4. Error of count is great where bacteria 



are very few or many. 



5. Cannot be used for quantitative work 



when the bacteria are few in number. 



6. Many fields must be counted, because 



of the uneven distribution, if an accu- 

 rate count is required. 



7. Large, compact clumps cannot be 



counted. 



8. Bacteria may be lost in process of pre- 



paring slides. 



1. All bacteria do not grow on the plates 



because of changes in food, tem- 

 perature relations, or other con- 

 ditions of environment. 



2. The difficulty of breaking up the 



clumps in the milk affects the accu- 

 racy of the count. 



3. Requires from 2 to 5 days' incubation 



period. 



4. Different species require different in- 



cubation temperatures. 



5. Gives no idea of the morphology of the 



organisms present. 



6. More apparatus required, therefore 



more expensive. Technique com- 

 plicated and difficult for trained 

 bacteriologists to use in such a way 

 as to secure consistent results. 



ADVANTAGES. 



1. Less apparatus required, therefore less 



expensive. Technique simple. 



2. The results on a given sample can be 



reported within a few minutes. 



3. Shows the cell content, the presence 



or absence of streptococci and other 

 important things necessary in esti- 

 mating the sanitary quality of milk. 



4. Gives a better idea of the actual num- 



ber of germs present. 



1. Is necessary for isolation of pure 



cultures. 



2. Gelatin shows the liquefiers and, if 



litmus is used, the acid-producing 

 bacteria. 



3. Shows character of growth. 



4. Shows living organisms only. 



