REGULATION OF SALE 183 



tion and the can.s are put into ice water in order to chill 

 the milk sufficiently. It is then poured into a tank and 

 mixed, thus making its composition uniform. Then fol- 

 lows a process of cleansing, wherein the milk is either 

 passed through a centrifuge, so constructed that the 

 cream and the milk are not separated, but only particles 

 of dirt are thrown out, or it is passed through a filtering 

 apparatus which holds back some of these particles. A 

 gravel filter is frequently used for filtering. This is a 

 tank which is filled with layers of gravel of different 

 degrees of fineness, through which the milk is slowly 

 forced. The gravel is cleansed daily by washing 

 and roasting. Only the particles of dirt are removed 

 by this i)ro('ess; the number of hacteiia is not appre- 

 ciably reduced. A filter made of numerous layers of fine 

 linen, tightly stretched, has been used successfully in- 

 stead of the gravel filter. The cloth part is renewed 

 aftei- each use. This method has, among others, the ad- 

 vantage that the filtering may take i)lace directly into 

 the can from which the milk is drawn off for sale, or the 

 ai)paratus may be so arranged that while the milk is 

 being filtered and run off, it is at the same time cooled. 



The " clarified " milk is put into metal cans or glass 

 bottles in which it is to be sold. This filling is sometimes 

 done automatically, so that incorrect measuring is not 

 possible, and sometimes by means of a machine similar 

 in construction to those used in filling beer bottles. 



If the milk is to be pasteurized, it is first filtered, then 

 run through the pasteurizer and over the cooler, into 

 the delivery can; or it is placed in the clean bottles or 

 cans that go into the pasteurizer or sterilizer (see page 

 139). 



The public will scarcely require ordinances contain- 

 ing exactly detailed regulations in regard to these differ- 

 ent processes. Generally it is required only that the 



