I40 THE BACTERIAL CONTENT OF MILK 



sentative of the time elapsing between milking and human con- 

 sumption of the milk — we may expect not only a commencing 

 diminution of organisms but a survival of the fittest, that is, the 

 most resistant. If saprophytic bacteria are present with patho- 

 genic, there is a struggle for survival, fortunately ending generally in 

 the survival of the saprophytic because the conditions in milk favour 

 these rather than pathogenic bacteria. Now whilst this is in part 

 due to competition owing to a limited food supply and an unlimited 

 population to which reference has been made, it is also due in part to 

 the inimical influence of one species or its products upon another 

 species or its products. This is known as antagonism amongst bacteria, 

 or antibiosis} And the antagonistic products are of two kinds. There 

 is first the toxin, which is of the nature of a ferment, producing in 

 many cases a local and a general effect when introduced into the 

 body of an animal. Secondly, there is what has been termed the 

 intracellular poison,\\h.\c\\ is a poison present in the body of the micro- 

 organism, and which may be a property common to several species.^ 

 These products, then, may in the course of forty-eight hours be 

 produced in milk, under favourable conditions, and greatly affect 

 the bacteria contained therein. This seems to us to be a matter 

 of the first importance, and one calling for a good deal more atten- 

 tion than it has hitherto received. But there is also another side to 

 this question. We have little doubt in our own minds that many 

 of those cases of milk poisoning occurring in children are due not 

 to the effect of ordinary milk bacteria, or indeed directly to bacteria 

 of any kind, in whatever numbers they may be present, but to the 

 chemical and organic changes set up by the production of toxic bodies 

 in milk which has stood for a long time since tnilking, and in which, 

 though there may be but one or two surviving species present, 

 there is a considerable amount of toxic substance accumulated. 



There is another natural effect of the passing of time upon 

 bacteria in milk which should not be lost sight of. As the struggle 

 for survival increases, and the pabulum becomes more and more 

 limited, and less and less favourable on account of toxic influence, 

 there is a tendency for some of the contained organisms to sporu- 

 late, a natural process the various stages of which may be sum- 

 marised as follows : — 



Spore formation. — When a bacillus is about to produce spores, 



1 There is some reason to suppose that symbiosis and metabiosis may also 

 occur amongst bacteria in milk, bringing about an inter-relationship between 

 them. 



2 Croonian Lectures of Royal Coll. of Phys., 1898. (Sidney Martin.) 



