288 EXPERIMENT STATION RECORD. 





While the absence of ammonia is therefore no proof of the purity of a sample, its 

 presence must be considered as an indication that the milk has been watered or 

 otherwise contaminated, and this method of examination therefore becomes of 

 importance from the standpoint of hygiene. 



Are nitrates eliminated by the mammary gland? M. Henseval and G. Mullie 

 (Rev. (u'n. Lait, 4 (190.5), No. 22, pp. 512-5 18). — The presence of nitrates in milk is 

 usually accepted as an indication of watering. 



In endeavoring to ascertain if nitrates are ever excreted in milk, the authors have 

 carried on experiments since 1903 with 20 cows, most of which were diseased. The 

 results with only 1 cow are reported in this preliminary note. This animal, which 

 was affected with actinomycosis, was given potassium nitrate, and the milk obtained 

 showed often, though not uniformly, the characteristic reaction of nitrates. 



The fat of top milks, J. W. England and C. H. La Wall (Jour. Amer. Med. 

 Assoc, 45 (1905), No. 13, pp. 893, 894).— Fat determinations by the Leffmann and 

 Beam method were made of the layer of cream in certified, guaranteed, and ordinary 

 bottled milk as sold by 8 or 9 dairies in Philadelphia. It is stated that marked 

 differences were found in the fat content of the cream from pint bottles as compared 

 with quart bottles, and for that reason pint bottles should never be used in obtaining 

 top milk for modification in infant feeding. 



Biological and biochemical studies of milk, C. J. Koning (Milchw. Zentbl., 1 

 (1905), Nos. 7, pp. 289-305; 8, pp. 338-356) .—The studies here reported in continua- 

 tion of previous work (E. S. P., 16, p. 817) deal with the acidity of milk. Among 

 the conclusions reached are the following: 



In market milk there is no definite relation between the number of bacteria and the 

 degree of acidity. The loss of carbon dioxid, through which the acidity is reduced, 

 is not replaced during the bactericidal stage by the production of lactic acid. Not 

 until the degree of acidity has passed a certain limit is there a definite relation 

 between the production of acid and the multiplication of lactic-acid bacteria. If, 

 however, sterilized milk is inoculated with lactic-acid bacteria there is a definite 

 relation between the acidity and the bacterial content. 



Infection from the air of the stable is of great influence in the souring of milk. 

 It is not possible to draw conclusions as to the age of a sample of milk from the 

 increase in acidity in a certain time at a definite temperature. In some investiga- 

 tions in Holland the morning's milk contained more bacteria than the evening's 

 milk. Prompt cooling lengthens the bactericidal phase and delays the decomposi- 

 tion of the milk. Cleanliness in milking and low temperatures in keeping milk are 

 essential in delaying souring. 



Any particular brand of commercial culture for the ripening of cream was not 

 found to be uniform in chemical composition, and many of the bacteria were found 

 to be dead or incapable of growth. 



Does centrifug-ing- lessen the number of bacteria in milk ? S. A. Severin 

 (Centbl. Bait, [etc.], 2. AM., 14 (1905), No. 18-20, pp. 605-615).— Counts were made 

 of the number of bacteria in samples of milk taken immediately before and after 

 (1) ordinary centrifugal separatiou, (2) separation with the centrifuge protected with 

 sterilized cotton to prevent entrance of bacteria from the air, and (3) before and 

 after centrifuging or shaking in closed bottles. The interval between the taking of 

 samples was about 15 minutes. 



The number of colonies developing on agar and gelatin plates was increased to a 

 marked extent by all three methods of treatment. Contamination from the air dur- 

 ing separation or shaking was therefore excluded as a cause of this increase. The 

 explanation offered by Dunbar and Kister that groups or clumps of bacteria which 

 develop as single colonies in the first instance appear as a greater number of colonies 

 on the second series of plates is not accepted by the author, who suggests instead that 



