SUMMARY OF CHAPTER VII 



ON THE CELLULAR CONTENT OF MILK 



THE presence of cells in milk has been known for many years. They 

 form a normal constituent of the milk obtained from healthy cows 

 under satisfactory conditions. It is a question whether the number 

 of cells which are present may enable a determination to be made 

 of the condition of the cow or of the cow's udder at the time of 

 milking, i.e. whether healthy or not. If the enumeration of cells 

 could be utilised for such a purpose, it would evidently be necessary 

 to ascertain within what limits the number of cells found could be 

 regarded as normal, and whether the boundary line denoting patho- 

 logical conditions could be defined. Further, it would be necessary 

 to ensure the use of an accurate method of estimation of the number 

 of cells present. 



Several methods have been suggested and used for estimating 

 the cellular content of milk. The most usual methods have been 

 to take a small quantity of milk, place it in small tubes, and centri- 

 fugalise for a definite period. The supernatant fluid is then drawn 

 off and the sediment investigated. This may be done either by 

 removing the whole of the sediment and making films of it, which 

 is known as the ' smeared sediment ' method, or the supernatant 

 fluid may be removed down to a certain point, the volume of 

 sediment being noted. This volume of sediment is then stained 

 and the cells counted in an ordinary blood-counting apparatus. 



Recently it has been stated that more accurate counts are 

 obtained when the milk is not previously centrifugalised but when 

 the counts are made direct from milk which has been thoroughly 

 mixed. Objections have been raised to the centrifuging of milk 

 on the ground that a large number of the cells are caught up with 

 the cream, becoming entangled in the meshes of the fat globules. 

 The cream being removed with the supernatant fluid after centri- 

 fugalising, a large number of the cells are removed with it, and do 

 not enter into the count subsequently made. This error is said 

 to amount to about 12 per cent, of all the cells, but it is probable 

 that considerable variations exist in the number of cells thus 

 caught up and removed from the fluid used for the estimation. 



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