284 BIOLOGICAL AND SANITARY MATTERS. 



practice of washing out tlie dairy vessels with a little water alter 

 milking, and adding this to the mUk, .prevails. The precautions 

 against this form of infection are also obvious, though more 

 4iflicult to carry out in practice than those mentioned above. 



Water Supply. 



A water supply which is not contaminated, nor liable to con- 

 tamination, and a good system of sanitation are necessary. 

 Before milk is supplied from a farm or dairy the water supply 

 must be rigidly investigated. The investigation may be con- 

 veniently divided into three parts. 



(1) Inspection of source. 



(2) Chemical analysis. 



(3) Bacteriological examination. 



Inspection of Source. 



The following sources of supply are almost always satis- 

 factory : — 



(1) Deep artesian borings. 



(2) Deep wells passing through an impervious stratum — e.g., clay. 



(3) Springs fed by an uninhabited watershed — e.g., springs in the sides 

 of hiUs. 



Public water supplies, mountain rills, and wells sunk in open 

 ground remote from habitations are very frequently — but by no 

 means always — of a satisfactory nature. 



On the other hand, shallow wells near dwellings, ponds, small 

 brooks, and wells in pervious strata — e.g., gravels — are usually 

 unsatisfactory. 



The following points must be considered to be highly unsatis- 

 factory : — The proximity of privies, cowsheds, etc. ; the trend of 

 the lands from habitations to the source ; faulty conditions of 

 the sides of a well (otherwise satisfactory), which may allow 

 surface drainage to enter ; and, except in the case of springs on 

 the sides of uninhabited hills, a marked diminution of the supply 

 after drought, and increase after rain. 



It is advisable to ascertain the geological formation, and 

 whether artificial fertilisers are much used in the vicinity ; if 

 this is done to a large extent, some of the chemical evidence 

 may be discounted. 



Chemical Analysis. 



Taking of Samples. — At least half a gallon of water must be 

 taken for the analysis ; a " Winchester quart " bottle is con- 

 venient for this purpose. The first portions — say, 10 to 20 



