DETERMINATION OF ACIDITY. 25 



In this table the figures in the top horizontal line indi- 

 cates the temperature of -the milk and those in the left 

 vertical line indicate the lactodensimeter reading. For 

 instance, if the areometer reading is 30 and the tempera- 

 ture is 16 degrees, the exact specific gravity may be found 

 in the ninth column and the sixth line from the bottom. 

 This figure 30.2 signifies a specific gravity of 1.0302. 



Other forms of apparatus described by Bischoflf, Reck- 

 nagel and Soxhlet, do not require the table of correc- 

 tions. They are provided with a thermometer without 

 the regular thermometric scale. The thermometer read- 

 ing is simply a correction number which must be either 

 added to or subtracted from the reading on the main 

 scale (see figure i). 



II. THE DETERMINATION OF THE RE ACTIOX AND 

 ACIDITY. 



The reaction of human milk in its normal state is alka- 

 line; the milk of carniverous animals is acid. Cow's milk 

 should, according to earlier investigator.'^, has an am- 

 photeric reaction. However, in a perfectly fresh condi- 

 tion, that is, at the moment it leaves the udder, cow's milk 

 reacts slightly acid (Vaudin). The reaction does not 

 change if the milk is placed in a hermetically sealed glass 

 tube and heated a long period at a temperature of 100 

 ■ degrees C. It becomes more strongly acid when allowed 

 to stand in the open air or even with the air excluded. 

 Through the action of bacteria (ferments) milk sugar is 

 converted into lactic acid (commonly called lactic acid 

 fermentation). OrdinariT)- inactive lactic acid is thus 

 produced, although the formation of active paralactic 

 acid has been observed by Gunther and Thierfelder. Oc- 

 casionally carbonic acid and ethyl alcohol are formed 

 (Leichmann). The acid production, which is favored by 

 high temperatures, ceases when a fixed amount of lactic 



