necessary to the production

Merely because an occupation involves a function not indispensable to the production of goods, in the sense that it can be done without, does not exclude it from the scope of the Fair Labor Standards Act. Conversely, merely because an occupation is indispensable, in the sense of being included in the long chain of causation which brings about so complicated a result as finished goods, does not bring it within the scope of the Fair Labor Standards Act.