P.ACTERIA IN CHEESE-MAKING. 257 



they are in small quantities and this great increase appears to 

 be wholly confined to the lactic bacteria. After a time, the 

 length of which is very variable, the bacteria begin to decline, 

 until finally only a comparatively small number are left. 



If the number of bacteria in ripening cheese be compared 

 with the number in ripening cream a great difference will be 

 found. In ripened cream, in the course of two days, the num- 

 ber per c.c. may be over 1,000,000,000; but in ripening 

 cheese the number hardly rises much above 100,000,000, and 

 this number is reached only after some weeks. The numbers 

 thus never approach those found in normally ripened cream. 

 This is doubtless due to the compact mass and the small 

 amount of moisture. It follows that bacterial action in cheese 

 will be less vigorous and less profound than bacterial action 

 in cream. 



Nevertheless this multiplication of bacteria in the cheese 

 cannot take place without producing some effect on the pro- 

 duct. What this effect is can only be stated in part. That 

 the bacteria are partly concerned in the chemical changes 

 we have already indicated. Among the bacteria are some 

 belonging to the class referred to on page 194, which have 

 the power of digesting curdled casein and converting it into 

 soluble products. It was supposed by Duclaux that these 

 bacteria were the chief cause of the digestion of casein which 

 occurs in the ripening cheese. But it has appeared, as 

 shown above, that these peptonizing bacteria do not grow to 

 any considerable extent in the cheese, the chief increase in 

 bacteria being in the lactic organisms. If bacteria do aid in 

 the chemical changes it would seem to be the lactic bacteria 

 that are concerned. 



Can the lactic bacteria contribute to the advancing digestion 



of the casein? Freudenreich, who has done more work upon 



this matter than any other investigator, finds that the lactic 



bacteria have the power of digesting the casein, and may con- 



22 



