Since then (1904) Miss Florence Durham has shown that if the skins of young or embryonic mammals (rats, rabbits and guinea-pigs) be ground up and extracted in water, and the expressed juice be then incubated with solid tyrosin for twentyfour hours, with the addition of a very small amount of ferrous sulphate to act as an activator, a pigmentary substance is thrown down.
Also occurring in flat oysters, where the eggs are incubated on the gills.
When fixed amounts of this dilution series are mixed with an appropriate agar and incubated, then different numbers of colonies will be obtained.
Culture results are available from the microbiology laboratory as soon as bacteria grow in a special plate incubated at temperatures at or above body temperature.
These ingredients are then added to the appliance, which keeps the yogurt gently incubated for hours at a time.