152 BACTERIA IN DAILY LIFE 



from the following extract from an American 

 report on the subject : 



"On the whole it is evident that the conditions 

 surrounding water when it freezes are very important 

 factors in determining the purity of the ice formed. If 

 there is a considerable depth of water in portions of 

 a somewhat polluted pond or river, and the ice is formed 

 in these portions in comparatively quiet water with but 

 little matter in suspension, this ice will probably be 

 entirely satisfactory for domestic use. On the other 

 hand, ice formed in shallow portions of such ponds 

 or rivers, even during still weather, or in any portion 

 if there is a considerable movement of the water by 

 currents or wind while it is forming, may be rendered 

 by these conditions entirely unfit for domestic use." 



We have learnt that ice contains bacteria, that 

 its bacterial contents are to a certain extent depen- 

 dent upon the bacterial quality of the water 

 before crystallisation, and that an important factor 

 in determining its purity is afforded by the 

 physical conditions prevailing at the time of 

 freezing. 



It will be of interest to ascertain in more detail 

 what effect the process of freezing has upon the 

 number of bacteria present in the water what 

 is the degree of bacterial purification effected 

 during the conversion of water into ice. 



Now Professor Uffreduzzi, in his investigations 



