THE DECOMPOSITION OF MILK 



143 



10. Record your results, noting the date on which the 

 plates were made, the age of the milk, the dilution, number 

 of colonies on the plate and the average number of organisms 

 per cubic centimeter. 



11. Examine in hanging drop and note the morphology 

 of the microorganisms producing the most predominant 

 types of colonies on each set of plates. Indicate after the 

 drawing, the comparative numbers on each set of plates 

 by the signs , + , +, + + , etc., to indicate absence, 

 presence of few, or many of the type. 



12. Note whether molds or yeasts are present on any 

 set of plates. Should either be found on fresh milk plates? 

 Why? What types of microorganisms would you expect 

 on fresh milk plates? 



13. Prepare your data according to the following dia- 

 gram: 



Average count per cc 301,470 



14. Plot the curve showing the change in acidity and one 

 illustrating the count per cubic centimeter on the same 

 paper, using different colored inks or different types of 

 lines. Use days for abscissae, acidity and count for ordinates. 

 Start at the same origin. 



15. Is there any relation between the change in acidity 

 and the change in flora? 



Should the acidity and count curves run parallel? If 

 they do not, give a reason why. 



How could the bacterial count be made to increase 

 after it goes down to a constant number? 



