But as these foodstuffs cannot be suddenly increased in the course of the year, their import grows, just as that of exotic foods in general (coffee, sugar, wine, etc.) and of articles of luxury. Hence excessive imports and speculation in this line of the import business. Meanwhile, in those branches of industry in which production can be rapidly expanded (manufacture proper, mining, etc.), climbing prices give rise to sudden expansion soon followed by collapse. The same effect is produced in the labour-market, attracting great numbers of the latent relative surplus-population, and even of the employed labourers, to the new lines of business. In general such large-scale undertakings as railways withdraw a definite quantity of labour-power from the labour-market, which can come only from such lines of business as agriculture, etc., where only strong lads are needed. This still continues even after the new enterprises have become established lines of business and the migratory working-class needed for them has already been formed, as for instance in the case of temporary rise above the average in the scale of railway construction. A portion of the reserve army of labourers, which keep wages down, is absorbed. A general rise in wages ensues, even in the hitherto well employed sections of the labour-market. This lasts until the inevitable crash again releases the reserve army of labour and wages are once more depressed to their minimum, and lower. [32]
Inasmuch as the length, great or small, of the period of turnover depends on the working period proper, that is, the period necessary to get the product ready for the market, it is based on the existing material conditions of production specific for the various investments of capital.
In agriculture they assume more of the character of natural conditions of production, in manufacture and the greater part of the mining industry they vary with the social development of the process of production itself.
Inasmuch as the length of the working period depends on the size of the supply (the quantitative volume in which the product is generally thrown upon the market as commodities), it is conventional in character.
But the convention itself has its material basis in the scale of production, and is therefore accidental only when examined singly.
Finally, inasmuch as the length of the turnover period hinges on that of the period of circulation, it is partly dependent on the incessant change of market conditions, the greater or lesser ease of selling, and the resultant necessity of disposing of part of the product in nearer or remoter markets. Apart from the volume of the demand in general, the movement of prices is here of cardinal importance since sales are intentionally restricted when prices are falling, while production proceeds; vice versa, production and sales keep pace when prices are rising or sales can be made in advance. But we must consider the actual distance of the place of production from the market as the real material basis.