22 VETERINARY HYGIENE 



whether or no the water is fit for drinking purposes. One analysis 

 of a particular supply may give very valuable information that 

 would lead to the condemnation of the water that would otherwise 

 pass without suspicion, notwithstanding the most careful examina- 

 tion of the source of supply. On the other hand pollution by 

 sewage may be, and often is, of an intermittent character. Such 

 intermittent contamination is sometimes of a very dangerous nature 

 to people if not to animals, and it may escape detection if the sample 

 for analysis is taken between the periods when contamination occurs. 

 A shallow well, for instance, after a long period of dry weather 

 may yield a water that by analysis would be described as " pure 

 and wholesome," but which, owing to faulty steining or other defect 

 in construction, might be seriously polluted with sewage matter 

 washed through the soil after heavy rain. A newly constructed 

 well would almost certainly be condemned if the potability of its 

 water is considered only on the merits of a sample taken before the 

 water that has collected during construction, and for some time 

 after, has been withdrawn. Time must be given for a new well 

 to cleanse itself. The examination of a water supply is not such 

 a simple process as many think. 



The methods used for the examination of water include Physical, 

 Chemical, Microscopical, and Bacteriological tests, and lastly the 

 Interpretation of the Results of the tests. 



Physical Examination includes the examination of the water 

 itself and the source of supply. 



Examination of Supply. The mere examination of the source 

 of a water is often in itself sufficient to condemn it without taking 

 the matter any further. The examination of the supply and its 

 surroundings is not, however, sufficient to pass a water as " pure 

 and wholesome." 



The veterinary practitioner should make it his business to note 

 the source of supply of the water on farms with which he may 

 be connected. It is true that to fully understand water supplies 

 and the possibilities of their pollution a more than passing know- 

 ledge of geology is necessary. But it is also true that with but 

 an imperfect understanding of geology the practitioner may acquire 

 much valuable information concerning the water supplies of his 

 district. 



If the water is supplied from the public water works, probably 

 all that the veterinary practitioner need do is to note its degree of 

 hardness. If very soft and acid, as when coming from moorland, 

 it is liable to attack lead, and if it is conveyed about the farm in 

 lead pipes it may be well to warn the proprietor of the risk involved. 



