238 MASS. EXPERIMENT STATION BULLETIN 187. 



Table L. — Streptococci Suspended in Milk Subjected to Clarification. 



I. Bacterial count of whole milk J Before clarification, 33.,000\., , . 



1- <■ J J- . i • ^ AT^ .ex- io^r,^ >ol per cent, decrease, 



before adding streptococci. ^After clarification, 16,000 J 



Bacterial count of same milk fBefore clarification, 29,000,000 \ . 



after adding streptococci. \After clarification, 36,000,000 J 



II. Bacterial count of whole milk f Before clarification, 75,000 1 . 



before adding streptococci. \ After clarification, 120,000 / 



Bacterial count of same milk fBefore clarification, 2,000,000 \ . 



after adding streptococci. \After clarification, 3,700,000/ 



Colonization of Bacteria in Milk. 



Little can be stated with any degree of assurance concerning coloniza- 

 tion of bacteria in milk. That colonization occurs, and that the degree of 

 colonization is irregular in different milks, can be attested in several ways. 

 One of these methods is set forth in what might be wisely designated as 

 the provisional conclusions offered by many of the workers who have 

 determined the number of bacteria before and after clarifying, assuming 

 that the increased count is due to the breaking up of the colonies formed. 

 This is, of course, indirect evidence, and must be regarded as tentative 

 until something more direct can be provided. Little is known of a definite 

 character concerning what bacteria wiU do in this respect, so that any 

 conclusions based upon this precarious factor may go far astray. Knowl- 

 edge of exact value upon this subject is almost entirely lacking. Again, 

 the tendency of bacteria to grow into colonies is daily recognized, and yet 

 there are conditions of cultures which do not favor such developments. 

 What can be said about milk, and to what extent does the colony vitiate 

 our crude plating methods and our comfortable conclusions based on 

 them? This is important and is made conspicuous by a shroud of 

 ignorance. 



Efficiency of the Individual Organism Free and in Colony. 



This leads to the next step, which is also of significance. Does the 

 individual organism in a colony exercise the same degree of physiological 

 efficiency as when the organism is alone and acting in an individual role? 

 We are told by Mclnerney^ that bacteria increased more rapidly in 

 unclarified than in clarified milk, yet a greater degree of change, as the 

 production of acid, is recorded in the milk influenced by clarification than 

 in the check culture unclarified and uninfluenced. This also occurs in a 

 pure culture of lactic bacteria when shaken. This suggests, possibly, 

 that per individual the clarified culture is doing greater work. What 

 values shall be attached to the individual germ free as against the 

 same germ in a colony? This we must know if we are going to interpret 



1 Mclnerney, T. J.: Clarification of Milk. Cornell Univ. Agr. Exp. Sta. Bulletin No. 389, 

 April, 1917. 



