xi EXAMINATION OF MILK 201 



A second objection is that the sediment is not all manurial 

 matters, but a considerable part is composed of substances 

 natural to milk, such as cellular elements, and also harmless 

 inorganic bodies like sand, and these are a variable part of 

 the whole. 



A further objection is that the amount is directly pro- 

 portional to the efficiency of straining rather than to the 

 cleanliness precautions adopted. This is the most important 

 of the objections to this estimation, since straining, while it 

 removes the larger dung particles, does not remove the bacteria. 

 This being the case, a milk collected under extremely unsatis- 

 factory conditions as regards cleanliness of sheds, cows, milkers, 

 and milk vessels, but very carefully strained, might show con- 

 siderably less sediment than a sample of milk collected under 

 far superior conditions as regards general cleanliness but only 

 rapidly strained through coarse muslin. 



Straining as a purification process is most irrational. 

 The dung gives up a large part of its bacterial content to the 

 milk, the only part of it which is prejudicial, and the residue 

 is then strained off. Orr 1 made numerous estimations of the 

 amount of sediment, and concluded that " there is no relation- 

 ship between the amount of sediment and the number of 

 bacteria present." This is what might be anticipated. 



There is a further objection to the use of a standard based 

 upon the amount of dirt in milk. If one is set up it is 

 inevitable that the farmer and the milk purveyor will imagine 

 that the dirt itself is at fault and the thing to avoid, and 

 therefore all that is required is to filter off the dirt and deposit 

 by improved filtration processes. Cleanliness will be neglected 

 on the supposition that purification by filtration can come 

 afterwards. 



The writer is of opinion that the measurement of the 

 sediment or dirt (as it is often called) in milk is an estima- 

 tion which it is of no material value to retain. It gives no 

 information which cannot be obtained much better in other 

 ways, while it is open to many and serious sources of error. 

 Take care of the bacteria and the sediment can take care of 

 itself. 



1 Report on Milk Contamination, 1908. 



