292 THE MILK QUESTION 



temperature. If the milk sours in this time and curdles 

 normally, it may be taken as an indication that antiseptics 

 had probably not been added. On the other hand, if it does 

 not curdle in this time under these conditions, it may be 

 regarded as possibly containing preservatives, and a 

 systematic search, to determine which preservative has 

 been added, should then be made by the methods of Leach, 

 Van Slyke, and other well-known authorities on the sub- 

 ject. 



Other methods of preserving milk. Various other methods 

 have, from time to time, been suggested for the preserva- 

 tion of milk, such as actinic rays, the electric current, 

 pressure, etc. 



The actinic rays comprise the violet and ultra-violet 

 portions of the spectrum. In other words, they are the 

 light rays of shortest wave length. These rays are not 

 ordinarily visible to the eye, but are exceedingly active 

 germicides and have potent power in other directions. 

 They are the rays that burn the skin when exposed to the 

 sun, that hasten the hatching of frogs' eggs, that turn the 

 sunflower to the light, that act upon photographic nega- 

 tives, etc. In fact, they are rays of great potency. In 

 proper concentration these rays are exceedingly powerful 

 germicides. Water may practically be sterilized by sub- 

 jecting it to the influence of these rays, and the method is 

 now in actual use. The action of these light rays upon milk 

 is less satisfactory on account of the opacity of the milk. 



Milk subjected to electric currents, with the production 

 of electrolytic salts, and milk subjected to great pressure 

 have a certain amount of germicidal action, but the pro- 

 cesses are not practical, nor are they satisfactory to the 

 sanitarian. 



The proper preservation of milk. The only proper preserv- 

 atives for milk are cold and cleanliness. 



Cold adds nothing to the milk; it takes nothing away. 

 It does not change the composition or quality of the milk; 



