Februakt 9, 1906.] 



SCIENCE. 



211 



of all kinds of putrefactive bacteria and 

 disease germs, while milk which contains 

 B. lactis acidi soon has all other forms de- 

 stroyed by the acid or the growth of the 

 lactic bacteria, and, further, when we dis- 

 cover that every properly ripened lot of 

 cream with the most desirable flavor, and 

 every normally ripening cheese, has from 

 90 to 99 per cent, of this organism present. 



The Microscopic Estimate of Bacteria in 



Milk: Francis H. Slack, M.D., First 



Assistant Bacteriologist, Boston Board 



of Health Laboratory. 



The special apparatus used for centrif- 

 ugalizing the milk samples consists of an 

 aluminum disc and covers ten inches in 

 diameter and five eighths inch in depth, 

 fitted to hold twenty small glass tubes, 

 arranged radially. These tubes hold about 

 two cubic centimeters each and are closed 

 at both ends with rubber stoppers. 



The samples in the tubes are eentrifugal- 

 ized ten minutes at a speed of 2,000 to 

 3,000 revolutions a minute, thus collecting 

 the whole sediment from each sample on 

 the outer stopper. 



The sediment is obtained by breaking up 

 the cream, pouring out the milk and care- 

 fully removing the stopper with the ad- 

 hering sediment, not allowing any milk to 

 run back on the sediment to disturb it. It 

 is then evenly smeared with a drop of 

 sterile water over a space of 4 sq. cm. on 

 a glass slide, dried and stained with 

 methylene blue. 



Microscopic examination shows the ap- 

 proximate number and morphology of bac- 

 teria present as well as the presence of pus 

 and streptococci. 



The number of bacteria found in a rep- 

 resentative one twelfth oil immersion field 

 bears a fairly constant relation to the 1- 

 10,000 plate culture (grown for twenty- 

 four hours "in a saturated atmosphere at 

 37° C, 1 per cent, agar being used with 

 a reaction of -|-1.5). 



Thus, as a rough estimate, each coccus, 

 bacillus, diplococcus or chain in a repre- 

 sentative one twelfth oil immersion field 

 represents 10,000 bacteria to a cubic centi- 

 meter in the sample of milk examined. 



Advantages are : rapidity of examina- 

 tion, accuracy, easily learned technique, 

 lack of costly apparatus. 



The writer believes the method can, in 

 experienced hands, safely be iised for certi- 

 fying milk, certifying those samples in 

 which no bacteria are found, the large 

 number of samples which could be exam- 

 ined and the increased efficiency of the 

 supervision more than compensating for a 

 slightly greater accuracy in plate counts. 



The Quantitative Determination of Leuco- 

 cytes in Milk: Archibald R. Ward, 

 University of California. 

 The determination of leucocytes in milk 

 has been suggested by several writers as a 

 means for the detection of dairies market- 

 ing milk from cows with inflamed udders. 

 A series of duplicate determinations from 

 the same sample of milk were made by the 

 method of Doane and Buckley, of the 

 Maryland Agricultural Experiment Sta- 

 tion, College Park, Md., and by the method 

 described by Dr. Stewart, of the Philadel- 

 phia Bureau of Health. The Doane-Buck- 

 ley method gave more satisfactory results 

 with duplicate determinations than did 

 that of Dr. Stewart. The numerical re- 

 sults by the Doane-Buckley method varied 

 from four to forty times higher than those 

 obtained by the Stewart method. 



Kinds of Bacteria concerned in Souring 

 of Milk: P. G. Heinemann, University 

 of Chicago. 



All so-called lactic acid bacteria belong 

 to two groups, the colon aerogenes group 

 and streptococcus group. This arrange- 

 ment is arrived at by a comparative study 

 of culture characteristics of pathogenic, 

 sewage, fecal and milk streptococci. The 



