STERILIZATION OF MILK. 95 



other hand, prefer a slightly alkaline reaction. That dry organic 

 matter is less liable to decay than damp is well known, and also 

 that not only the products of the action of bacteria, but also many 

 other stuffs, such as alkalies, in a state of strong concentration, 

 carbolic acid, corrosive sublimate, chlorine, bromine, sulphurous acid, 

 &c., exert a poisonous action on the bacteria. Many bacteria, espe- 

 cially those of the aerobic sort, are only able to live in the presence 

 of a plentiful supply of free oxygen. Others, the anaerobic kind, on 

 the contrary, as Pasteur first pointed out, require, for their develop- 

 ment, the absence of free oxygen; while lastly there are others, the 

 facultative anaerobics, which can exist under both conditions. 



40. Sterilization of Milk. It has been known since the year 

 1884 that sterilized milk, to which no sugar had been added, 

 enclosed in hermetically-sealed tin vessels, has been known which 

 could be kept perfectly well, and without losing its value, for use 

 on board ship and for export to foreign countries. On the other 

 hand, the great advantages of sterilized milk as an article of food, 

 especially for the feeding of children, have not till recently been 

 recognized. Its preparation has been first rendered possible by the 

 work of Hueppe, and through the indefatigable, inventive, technical 

 genius of Soxhlet. 



After what has been stated in 39, the question presents 

 itself as the theoretically very simple one of destroying the low 

 organisms in milk. Were the question only the destruction of 

 vegetative cells, the continuous heating for 15 minutes at a tem- 

 perature of 75 C. would be sufficient. This treatment is known 

 as Pasteurizing. This is of exceptional importance for milk con- 

 taminated with pathogenic germs. The more important kinds of 

 this type of germ, viz., those causing tuberculosis, typhus, and 

 cholera, form, so far as present researches show, no lasting spores, 

 and succumb therefore to very low temperatures. In the case of 

 many spores of different kinds of saprophytic bacteria, however, 

 which often occur in milk, and which impair to a very large extent 

 its keeping properties, the only way to destroy these effectually 

 when they are present is by means of a comparatively high 

 temperature, either by simple or intermittent sterilization. 



Milk is sterilized in the full sense of the term only when it has 

 been rendered entirely free from germ-life by sufficient heating, that 

 is to say, when all the lower forms of life which it contains, vegeta- 

 tive forms as well as lasting forms, are entirely killed, and any 



