Device for pneumatically milking a cow, comprising a number of milk extractors, each comprising a teat cup as well as milk line connected to the lower end of the teat cup, which line leads from the teat cup to a collection chamber for the milk from the teat cup, each milk extractor being provided with a supply for a cleansing medium, such as a disinfectant, to the teat cup, in particular to a teat present in the teat cup, the supply comprising a line having an end portion with discharge end, and each milk extractor being provided with means for closing off the passage of the milk extraction at or downstream of the discharge end of the line for cleansing medium, preferably at that level, when discharging the cleansing medium, the closing means comprising a reciprocating closing body that can be moved between a position leaving the passage of the milk extractor free and a position closing it off, the closing body being provided with a squirt line forming the end portion with discharge end of the line for supply of cleansing medium, and being positioned to debouch into the milk extractor, particularly the milk line, when in the closing-off position.