STERILIZATION OF MILK. 155 



kinds have, however, arisen also here. First of all, per- 

 fectly satisfactory condensing-cans have not been obtained. 

 Those applied by Dahl were of sheet iron, and were made 

 air-tight by soldering the cover on. The weak points of 

 these cans are, that they can only be used once when the 

 can is once opened the milk will spoil comparatively soon ; 

 and they are, rather expensive to be used for so cheap an 

 article as milk. Glass bottles would be far better in many 

 respects, but they are so easily broken during the heating 

 as to greatly increase the expense of the sterilization. 



Like ScherfPs method, that of Dahl has been modified 

 in many ways without any really practical and reliable 

 method for the preservation of the milk having, to my 

 knowledge, yet been found. The difficulties which have 

 not yet been overcome are partly that the proper preserv- 

 ing cans come too dear, partly that the milk is not com- 

 pletely sterile, or else must be heated so high that it 

 assumes a disagreeable cooked taste, and is changed in 

 quality and appearance. Different apparatus have been 

 constructed, and preserving-cans of the most varying kinds 

 have been invented and improved. [Among German 

 methods which have given satisfactory results in practice 

 may be mentioned that of Neuhaus, Gronwald, and Oehl- 

 mann (see Weigmann, " Milchconservirung," 1893, p. 47). 

 In the investigation made by Petri and Massen in regard 

 to milk sterilized by this method they found, however, 

 among the six hundred bottles examined " a large num- 

 ber of bottles" containing living bacteria.*] Patents in 

 large numbers have been granted in different countries, 

 and each inventor has claimed with confidence that the 

 problem has been solved, and that his apparatus and 

 method may be successfully applied anywhere. 



The bacteria found in milk during different seasons 

 * Author's addition to American translation. 



