1902-3.] Bacterial Contamination of Milk. 485 



respect inferior to the samples of milk drawn by hand, in fact, if any- 

 thing, rather superior in point of flavour. The judges regarded the 

 Murchland machine as a practical success. On the other hand, the 

 chief defect in the Thistle Milking Machine was the effect it had upon 

 the keeping qualities of the milk. Most of the samples from it de- 

 veloped sourness in twelve to twenty-four hours, while samples drawn 

 by hand from the same cows at the same time, and kept under precisely 

 the same conditions, remained perfectly sweet for from thirty-six to 

 fifty hours. 



The Murchland Machine was also placed in competition for a prize 

 of ^5^50 at the York meeting of the Royal Agricultural Society^^ at York. 

 In the opinion of the judges it presented such difficulties for efficient 

 cleaning, that they were unable to report that it adequately fulfilled the 

 requirements set forth in the regulations for these trials. No award was 

 made in the competition. 



Cleaning Milk by the use of a Gravel Filter. 



The gravel filter in most general use is the model used by the 

 Copenhagen Milk Supply Company, (see Figs, g and 10). It consists 

 of two enamelled iron tanks placed at different levels ; a pipe in the 

 form of a siphon has its long limb connected with the bottom of the 

 upper tank, and its short limb with the bottom of the lower tank, so 

 that the milk poured into the upper tank comes up as a kind of spring 

 at the bottom of the lower one. On the bottom tank there are three 

 layers of gravel, that in the lower layer being about the size of a pea ; in 

 the middle layer somewhat smaller, and in the third or top layer, a little 

 larger than a pin's head. The layers are separated from each other by 

 perforated tin trays. On the top of the uppermost layer of gravel are 

 five thicknesses of fine cloth. The whole is kept in position by a 

 pyramidal frame- work which presses down the tin trays. As the milk 

 rises to the top of the tank, it passes into a large storage or mixing 

 receptacle. These filters require the most careful management, and are 

 generally taken to pieces immediately after use, when the gravel is 

 washed in hot water until the water comes off clean. It is then steamed 

 at a temperature of 202° F., after which it is spread out in shallow trays^ 

 and baked at a high heat. For the concluding operation, the gravel is 

 placed in a winnowing machine, which drives off all particles of fine dust. 



Schuppan^^ seems to have first called attention to the use of gravel 

 filters as a means of reducing the number of bacteria in milk. He 



