398 
Micro-organisms and their Action 
Cheese. 
All that has been said in the previous pages points to one 
thing, viz., the desirableness of preventing the occurrence of 
chemical changes in milk and butter. The safest plan to avoid 
those changes would be to remove their original cause, and as 
we have recognised the causes of the most prominent alterations 
in micro-organisms, the latter, with the decompositions and 
deteriorations Avhicli they involve, should be kept out as much 
as possible. That in the ordinary course of things we cannot 
shut out micro-organisms altogether has been pointed out ; but 
what we can do is to keep them in check to some extent, 
avoid some, and counterbalance the action of others. 
With cheese the case is widely different. Cheese is a product 
of fermentation from beginning to end. Not only is it a 
fermentative process by which the casein of milk is coagulated, 
and thereby separated from the watery part, but those changes 
which are comprised under the term ripening, and which 
virtually consist in transforming curd into cheese, are decompo- 
sitions brought about by micro-organisms, i.e., true fermen- 
tations. 
In cheese-making, then, the exclusion or destruction of micro- 
organisms would be entirely out of place : in fact, could it be 
done, it would make the manufacture of cheeses as we know 
them an impossibility. 
It must not be inferred from this that the more micro- 
organisms there are present in milk or curd the better suited it 
is for cheese-making, and the easier is the manufacture. We 
have seen that not all micro-organisms are able to develop 
under similar conditions, and in consequence do not bring 
about the same decompositions in similar media. We have 
further seen how a particular kind of micro-organism induces a 
certain fermentation with definite products, while other kinds 
give rise to other fermentations as recognised by the production 
of totally different compounds. Curd, then, though like^ milk, 
apparently a good soil for the majority of micro-organisms, 
is undoubtedly better suited to some than to others. The 
former will, under favourable conditions, develop and crowd 
out the latter. By changing the conditions they may become 
more favourable to another kind again, and the operator 
then has it, to some extent, in his power, by his mode of 
operation, to encourage the development of one or of another 
kind of micro-organism, and thereby produce cheeses of very 
different character. If we select from handbooks on cheese- 
making, in which hundreds of various kinds of cheeses are 
enumerated, those kinds only which are of a well-defined and uni- 
