EXPERIMENT STATION REPORTS. 249 



I cannot speak too highly of Mr. Cooledge's achievements in the 

 brief time that he has been able to devote to the new studies. His re- 

 sults fully justify the radical change in the project. He reports on his 

 work as follows : 



"During the past jeav I have been relieved from teaching and my 

 entire attention has been given to experimental work. The methods for 

 determining the keeping quality of milk and the bacteriological con- 

 dition of other daiiT products are so inadequate that an attempt has 

 been made during the past year to find a method which would give an 

 index of the actual ability of the bacteria and enzymes present in a 

 sample to produce the changes which are of interest to the dair-yman 

 and consumer. The outcome of this work, a paper, ''The Keeping Qual- 

 ity of Milk as Judged by the Colorimetric Hydrogen-ion Determina- 

 tion" by L. H. Cooledge and K. W. Wyant, was published in the March, 

 1920, Journal of Dairy Science. Short articles describing the method 

 have been published in the Quarterly bulletin and various dairy pub- 

 lications. The development of this new method has made it possible to 

 accumulate a large amount of data upon the action of bacteria in the 

 various dairy products. 



The advantages of this method are: 



The method provides a simi)le and accurate means of measuring the 

 activity of bacteria and enzymes present in the milk. The principal 

 advantages over methods now in use are mentioned below. 



The method does not measure the number of dead, inert, or living 

 bacteria present in a sample of milk but does measure the ability of 

 any enzymes or bacteria present to bring about changes. 



The poorer samples of milk may be picked out at the end of one 

 hour and the best samples given their i^roper grade at the end of eight 

 hours. 



The poorer the keeping quality of the milk, the sooner the results are 

 obtainable. 



The cost for material is one tube of broth for each sample tested. 



There is no expensive equipment necessary. 



A trained technician is not required. Any intelligent person may be 

 trained to grade milk by this method in a few days time. 



Over a hundred samples of milk may be easily examined each day if 

 the comparator designed by Cooledge is used. 



These advantages should make this method of valuable aid to city 

 milk plants, condenseries, ice cream factories, cheese factories, and 

 city, town and village health departments. 



By this method it is an easy matter to determine which of a dairy's 

 patrons are delivering an unsatisfactory milk. Advice in regard to san- 

 itation may then be given where it is needed without causing the ill 

 feeling which results from giving advice to the patron delivering a 

 good grade of milk. 



In order to make rapid determinatious or hydrogen-ion concentration 

 by colorimetric methods, the writer found it necessary to develop a 

 new comparator which is descril)ed in tlio May, 1!)2(), Journal of In- 

 dustrial and Engineering Chemistry. This com])arator will soon be 

 placed upon the market by the Central Scientific Co. A combination 

 comparator and rack for storage has been devised and with a set of 

 standards covering the range (»f pH necessary in the study of milk 



