New York Agricultural Experiment Station. 



d; 



In order to simplify the presentation the numerical results 

 given in this publication are those obtained after an incubatioD 

 for five days at 20-23° C. followed by two days at 37° C. unless 

 otherwise stated. 



EFFECT OF INCUBATION TEMPERATURE ON THE COUNT. 



The periods of incubation officially recommended are five days 

 at 21° C. or two days at 37 °C. The lower temperature is or- 

 dinarily chosen, since gelatin, which is preferred in qualitative 

 work on account of its better differentiation of colonies, will not 

 remain solid at the higher temperature. 



The accuracy of this five-day incubation of agar plates was 

 tested as follows : Samples were collected at the beginning, middle 

 and close of the milking, from each quarter of the udder of five 

 cows and plated on agar. Counts of the plates were made after 

 incubating five days at 20-23° C. and again after two additional 

 days at 37° C. The percentage of increase found at the second 

 count of the 18 samples from each quarter is given in Table I. 



Table I. — Variation in Bacterial Count after Additional Incubation 



at 37° C. 



Remark. — Letters R. P., R. B., etc., indicate, respectively, the right front, right 

 back, left front and left back quarter of udder. 



From the above table, which gives the results from a study of 

 360 samples of milk, it is seen that the effect of incubation at 

 higher temperature is most marked in the milk from Hammond 

 No. 2 and least in that from Carey F. 



