676 EXPERIMENT STATION RECORD. 



Casein media adapted to milk analysis, S. H. Ayers (pp. 229, 230). — A method 

 of prepiiring casein media is given, wliieh is thought to be of considerable value 

 in bacteriological milk analysis. A study of the bacterial growth upon casein 

 agar and on infusion agar led to the following results : 



" The 24 hours' count at 37° on casein agar was almost always lower than on 

 infusion agar when raw milk is being examined. When pasteurized milk was 

 examined the casein plates showed a higher count in 37 per cent of the samples. 

 After 6 days' incubation at 30° C, out of 50 samples of raw milk plated. 44 per 

 cent of the samples showed higher counts on casein agar. With 50 samples 

 of pasteurized milk, 78 per cent of the samples showed a higher count on casein 

 agar. From a study of the bacteria from about 50 samples of both raw and 

 pasteurized milk it seems that acid-forming bacteria do not develop quite as 

 well on casein agar. It does, however, favor the growth of the alkali formers, 

 the peptonizers, and inert bacteria. 



" The number of peptonizing bacteria in a sample of milk may be determined 

 directly from a casein agar plate. After counting the plate it should be flowed 

 with tenth-normal lactic acid ; this causes the precipitation of the casein, giving 

 a white opaque plate except where the casein has been dissolved about a colony 

 of peptonizing bacteria. There is then left a clear zone around the colonies of 

 peptonizing bacteria which enables one to determine their numbers in the sample 

 of milk under examination. It has been found from a study of a large number 

 of samples that this method of determination is accurate." 



A study of gas-forming bacteria in milk, L. A. Rogers and B. J. Davis (pp. 

 230, 231). — Cultures of gas-forming organisms were isolated from milk and 

 milk products in various parts of the country, and studied with special reference 

 to the relation to the fermentation of carbohydrates and the amount of gas and 

 ratio of hydrogen to carbon dioxid. When plotted on the frequency basis this 

 ratio gave four more or less distinct nodes. The proper classificatiou of the 

 cultures showed a close relationship between the ratio and the amount of gas. 

 The gas ratio was further correlated in some cases with the fermentation of 

 certain carbohydrates. 



" The group giving a ratio 1 : 1.6 to 1 : 2 shows a distinctly greater ability to 

 ferment saccharose, raffinose, and starch than the group giving the ratio 1 : 1.1. 

 It is probable that these tentative groups are somewhat heterogeneous and that 

 further refinement by the use of new test substances will bring out sharper 

 distinctions." 



Some actions of micro-organisms tijjon the constituents of butter, C. W. Brown 

 (p. 231). — One lot of butter was made from cream pasteurized at from 160 

 to 170° F., while the other was not pasteurized. Both the churn and butter 

 were placed in storage at from — 3 to -f3°. Fifty-seven species of bacteria 

 and 31 species of yeast, besides molds, were isolated. 



It was noticed " that 24 of the bacteria and 15 of the yeasts will grow on 

 12 per cent salt at 20° C. Four of these bacteria and 6 of these yeasts grow 

 well on 12 per cent salt at 6°. The ratio of the number of species of liquefying 

 bacteria to the number of nonliquefying bacteria isolated from ordinary agar 

 is the same as the liquefying to the nonliquefying isolated from 12 per cent 

 salt agar. Twelve per cent of salt has a much more inhibitive action upon 

 the species of liquefying yeasts than it does upon the nonliquefying. The 

 lactose in both the pasteurized and unpasteurized butter decreased from 0.315 

 per cent and 0.325 per cent to 0.285 per cent and 0.290 per cent, respectively, in 

 428 days; 50 per cent of the decrease in lactose took place within tlie first 10 

 days; when the butter was taken from storage at the end of 428 days and 

 placed at room temperature very little further decomposition of lactose oc- 



