We started Chapter 9 with a discussion of dirty milk. The measurement of sediment was a central concern of milk hygiene at the turn of the twentieth century but, as we saw, the definition of clean milk gradually changed in the following decades to become principally bacteriological. In this chapter we find that bacteria gained a curious kind of power, to the extent that the regulation of cleanliness in the milk industry from the First World War onwards was, and still is, dominated by counting these organisms. The microscopic world gained a privileged status and what had been called ‘visible dirt’ became invisible again. Bacteria were dutifully cultured on Petri dishes, like crops in miniature fields, and politicians then set limits of the number that were acceptable in any particular sample. The bacteria in these statements were usually undifferentiated, although by the First World War increasingly sophisticated science had become available to comment on the significance of the individual species. The underlying assumption of what we might call bureaucratic bacteriology was that the more bacteria there were, the worse it was for the consumer. Interestingly, this is still one of the quality criteria for milk in the milk regulations of the present day, now known as the Total Bacterial Count.