346 PRESERVATIVES MILK POLLUTION 



alkalinity, would not improve the character of the curd when it is 

 formed. Another somewhat curious fact is that cows' milk contains 

 more lime than an equal volume of lime water (which contains about 

 O13 per cent), so that the idea that the addition of lime water aids in 

 supplying materials for the formation of bone is founded on a mis- 

 conception. 



Other Methods of Preserving Milk. As already stated, it is 

 possible to prevent the growth of micro-organisms in milk by the 

 addition of antiseptics, and this is often practised, especially in hot 

 weather, when their growth is apt to be very rapid. The chief anti- 

 septics employed in preserving milk, butter and cream are 



Boric acid or borax, H 3 BO 3 , or Na,B 4 7 .10H,O. 



Salicylic acid, C H 4 (OH)COOH. 



Formaldehyde, H 2 CO, generally as "Formalin". 



The use of preservatives of any kind is probably not a wholesome 

 practice, for though the growth of most of the micro-organisms is pre- 

 vented, all change is not stopped. Moreover there is considerable 

 probability that, with children particularly, the use of preservatives 

 is attended with danger to digestion. Many of the substances used 

 as preservatives have been shown * to have an injurious action upon 

 digestive enzymes. 



Sodium carbonate or bicarbonate is sometimes added to milk as a 

 preservative. In reality it does not thus act, but merely prevents the 

 lactic acid, formed by fermentation, from coagulating the casein, and 

 by neutralising the acid as fast as it is formed, probably aids the change 

 of the sugar into lactic acid. 



Milk as a Medium for the Spread of Disease. Milk is peculi- 

 arly well fitted as a nutrient for the growth of micro-organisms. As 

 has already been stated, the number of organisms present in ordinary 

 samples is enormous. Fortunately, the majority of these bacteria are 

 harmless so far as their effect upon health is concerned, but unfortu- 

 nately milk very readily acts as a conveyer of pathogenic organisms. 



Diphtheria, scarlet fever, typhoid and especially tuberculosis' 2 

 have been in many instances communicated by milk. Careful Pas- 

 teurisation of all milk is greatly to be desired, and already dairies are 

 being started in various parts of England in which the milk is sub- 

 mitted to a modified Pasteurisation. The milk is heated in bulk to a 

 temperature of 60 to 65 and maintained at this temperature for twenty 

 minutes, then quickly cooled and sent out to the consumer, best in 

 closed glass bottles. Eussell has shown that the tuberculosis bacillus 

 may be destroyed by heating to 60 for twenty minutes, provided the 

 milk is heated under such conditions (with constant agitation and in 

 a closed vessel) as to prevent a pellicle forming on the surface. 3 The 



1 Leffrnann, Jour. Franklin Instit., 1899, 97. 



2 It has recently been asserted that bovine tuberculosis is probably not com- 

 municable to man ; but, though the opinion is that of the great authority, Koch, it 

 is not yet generally accepted. 



a Vide The Times, Feb. 25th, 1901. 



