GERMICIDAL ACTION 105 



organisms had aggregated into clusters under the influence of 

 agglutinins. The so-called germicidal action was also found to 

 be specific but the specificity of different samples was variable. 

 Further proof of the fact that this phenomenon must be attrib- 

 uted to agglutinins rather than to bacteriolysins was found in 

 the behaviour of heated milk. Heating to 56° C. for thirty 

 minutes, a condition which destroys bacteriolysins, weakens 

 but does not entirely inhibit the action ; it is entirely destroyed 

 at 75° C. 



St. John and Pennington ^^ found that milk, after heating 

 to 79° C. for twenty minutes, not only failed to show an ap- 

 parent diminution in the number of organisms but also showed 

 a much greater rate of bacterial development throughout the 

 period of observation. They point out that this is a serious 

 objection to pasteurisation as a reinfected heated product 

 exerts no restraining effect upon the invading organisms and 

 may, therefore, be more infective than raw milk receiving the 

 same original contamination. 



Stocking,2o who investigated this question, concluded that 

 the apparent diminution of organisms capable of development 

 on solid media was really due to bacteria finding the milk a 

 pabulum to which they are unaccustomed and consequently 

 died at a faster rate than they could multiply; he found that 

 this resting stage was scarcely observable with cemmon lactic 

 acid organisms which appeared to develop more or less rapidly 

 and continuously from the moment of their introduction into 

 the milk. The absence of a '' germicidal effect " with common 

 lactic acid organisms was confirmed by Rosenau and others and 

 supports rather than impairs the validity of the agglutination 

 hypothesis by accentuating its specificity. The resting stage 

 pointed out by Stocking must also be a factor, but cannot 

 wholly account for it as it fails to explain the comparative 

 absence of the phenomenon in heated milk unless it is assumed 

 that heating has resulted in chemical changes that have pro- 

 duced a more favourable environment for bacterial develop- 

 ment. Once this resting period or germicidal phase has passed, 



