548 



SCIENCE 



[N. S. Vol. XXXI. No. 797 



lactic-acid bacteria. Some fruit juices, like apple 

 cider, contain so much acid that nearly all kinds 

 of bacteria are unable to grow in them. Apple 

 juice contains about .72 per cent, of total acid. 

 Corn juice has about .25 per cent, of unknown 

 acid and some gallic acid(?). In corn juice 

 lactic acid bacteria grow profusely till about .35 

 to .45 per cent, of lactic acid is formed, when they 

 cease to grow. But yeasts are tolerant to much 

 larger amounts of acid and therefore continue to 

 grow in the corn juice till practically all the 

 sugar is used up. The alcohol formed is mostly 

 changed into acetic acid. In fresh silage large 

 numbers of yeasts and acid bacteria are found. 

 During the first twelve days of fermentation 

 nearly all of the biochemical changes are com- 

 pleted. The maximum growth of acid bacteria is 

 on the fourth day and the maximum growth of 

 yeasts is on the twelfth day. The highest tem- 

 perature of 29° C. was noted in the first 36 hours. 

 The samples were taken from a hole in the silo 

 five feet from the bottom, and from one to two 

 feet from the edge. 

 Further Studies in the Acidity of Fresh Milk: 



W. M. EsTEN, Storrs Agricultural Experiment 



Station. 



The entire range of variation of the acidity of 

 the milk in a year for a herd of cows numbering 

 more than twenty-five was from .155 to .187 per 

 cent. The law of variation is that the acid of 

 the milk varies inversely as the temperature. 

 Approximately on the first of February the milk 

 of all the cows is at its highest point of acidity. 

 On the first of August it is at its lowest point of 

 acidity. These two dates include the coldest and 

 warmest periods of the year. 



The variation during a lactation period proves 

 to be quite remarkable. An acidity of .48 per 

 cent, has been found at the first milking. In 

 from two to three days it falls to about .25 per 

 cent, from this figure, then gradually in about 

 three weeks to the normal, near .17 per cent., 

 which continues until about three weeks before 

 the end of the lactation period, when, at the last 

 milking, it falls to .12 or .13 per cent. The high 

 acidity at the beginning is explained by the fact 

 that the ash and salts are very much in excess of 

 the normal amount. Some of these are probably 

 calcium salts which are necessary for bone pro- 

 duction in the young animal. 



The quality of the milk varies as the acidity, 

 so that winter milk has more food value than in 

 summer and a higher price in winter is justified 

 by this fact. 



The acidity has an important bearing in the 

 inspection of milk. A dairy selling Jersey milk 

 with 5 per cent, of butter fat will sometimes show 

 an acidity of .20 per cent when fresh, and does 

 not then contain a particle of lactic acid. Under 

 these conditions the milk should not be condemned 

 for high acidity, but rather recommended for the 

 high acidity which indicates a high quality. It is 

 therefore requisite that milk inspectors be capable 

 of judging the high acidity of milk which indi- 

 cates high quality and value, from high acidity 

 caused by growth of acid organisms which pro- 

 duce lactic acid in milk of any quality. 



Bacteriological Methods in the Oyster Survey of 



Virginia: Meade Feeguson, Laboratories of 



State Board of Health of Virginia. (Read by 



title.) 

 Methods of Testing Shellfish for Pollution: 



Stephen BeM. Gage, Massachusetts State 



Board of Health, Experiment Station, Lawrence, 



Mass. 



The methods for testing shellfish for pollution 

 in Massachusetts have been devised to facilitate 

 the routine handling of a large number of samples 

 in the easiest and most accurate way. 



Collection of Samples. — Twelve to fifteen shell- 

 fish are collected from each sampling station, in 

 wide-mouth spring-top glass jars. The sampling 

 stations are distributed well over the area from 

 which shellfish are gathered, and samples of sea 

 water are collected from each station in addition 

 to the shellfish samples. 



Transportation of Samples. — Shellfish samples 

 should be delivered at the laboratory within 

 twenty-four hours after collection. Packing sam- 

 ples in ice is probably unnecessary, except during 

 very hot weather. 



Technio of Testing. — The individual shellfish is 

 washed with sterile water, opened with a sterile 

 oyster knife and a portion of the shell water 

 transferred to a fermentation tube. The body of 

 the shellfish is then removed from the shell, 

 washed with sterile water, opened with a sterile 

 scalpel and a portion of the alimentary canal 

 transferred to another fermentation tube. Ten 

 individual shellfish from each sampling station 

 are tested in this manner. 



B. coli Methods. — Dextrose pepton water is 

 used in the fermentation tubes. The incubation 

 of these tubes and the isolation and confirmation 

 of B. coli are in accordance with the standard 

 methods used in water analysis. No systematic 

 search is made for the sewage streptococcus, but 



