'8 



BULLETIN 782, IJ. S. DEPARTMENT OF AGlRlCULTURE. 



The results of the 14-4ay incti-b^'tk)!! are similarly shown in this 

 table. It will be noticed tk^t th^ alkaline change in 46 of the 68 

 cultures was dike %bM3^^ ^ the formation of alkaline carbonates and 

 -in thfe other 22 to tli6 presence of carbonates and ammonia. In 

 •alm'Ost every case the reduction in acidity was due largely to carbon- 

 ates and at the same time there was a considerable increase in the 

 amount of ammonia over that produced after 7 days' incubation. 

 Culture 107 after 14 days' incubation showed a smaller reduction of 

 acidity than after the 7-day period, indicating that there was a sec- 

 ondary acid fermentation. 



After 30 days' incubation the reduction in acidity in 24 cultures 

 was due entirely to formation of carbonates or bicarbonates, there 

 being no increase in ammonia over that contained in the control 

 tube of skimmed milk. In 37 cultures the alkaline change was due 

 to the combined action of carbonates and ammonia. It will be 

 seen, however, that in most cases the greater part of the change was 

 due to the alkaline carbonates. In general there was an increase 

 in the quantity of ammonia, found after 30 days, over that present 

 at the end of the 7 and 14 day incubations. Cultures 107 and 137 

 after 30 days' incubation were found to be more acid than the con- 

 trol cultures. Both these cultures showed an alkaline change after 

 7 and 14 days' incubation. In cultures 10, 12, 49, 113, 123, and 143 

 an excess of ammonia was found over that necessary to produce the 

 alkaline change, which showed that there must have been a secondary 

 acid fermentation. This is further substantiated by the fact that 

 these cultures showed a smaller change in alkalinity compared with 

 the control after the 30-day incubation than they did at the end of 

 the 7 or 14 day incubation. 



The results of the work shown in Table 2 are summarized in. 

 Table 3. 



Table 3.- 



-Cultures grouped according to reaction and cause of ulhali produx&^o-n in 

 sHm milk. 



Incubation 

 30° C. 



Reduction of acidity 

 due to— 



Increase of 



acidity 

 over control. 



Ammonia 



and alkaline 



carbonate. 



Alkaline 

 carbonate. 



Days. 



7 



14 



30 



Number of 

 cultures. 



10 



22 

 137 



Number of 



cultures. 



58 



46 



24 



Number of 



cultures. 











2 



1 Seven ammonia and no alkaline carbonate. 



This summary needs no discussion since it simply presents data 

 which have already been discussed. These results lead to the belief 



