OF WATER FOR ORGANIC MATTER. 41 



avoided ; but it may frequently be purified by some me- 

 chanical mode of separation^ such as simple straining. 



" If the water contains organic matter in solution, or a 

 condition approaching in all appearance to solution,, it may 

 be wholesome or unwholesome. The mere existence of 

 organic matter is no proof of impurity. We must know 

 if it brings animalcules or vegetable life or products of pu- 

 trefaction. We must know the quality as well as the 

 quantity. If the matter is peaty, consisting of the ordinary 

 humous class of acids and salts, the colour may be very dark 

 and the water very unpleasant to look at, without being in 

 any way, so far as I have ever heard, injurious to health, 

 although such water cannot be quite so wholesome as pure 

 water, since the oxygen of solution is diminished. The 

 taste and other sensible qualities will be the chief guides. 



^'If the matter is wholly or nearly colourless, it may 

 still be wholesome or unwholesome. It may, for example, 

 contain the juices of plants of a wholesome character. If 

 these juices are fresh, they may do no injury; but they 

 will not long remain fresh, they will putrefy. Water 

 containing organic matter ready to putrefy ought to be 

 avoided, as we cannot tell when the moment of danger 

 begins ; whilst the quality at best is never known to us 

 exactly. 



" To ascertain the nature of the organic matter, the water 

 is allowed to stand for a day or two, in which case it may 

 be found that organized bodies show themselves. Some- 

 times plants seem completely to fill the vessel, having come 

 out of a moderately clear solution. When standing, in 

 this case, the water must be prevented from evaporating, 

 and it must be in glass, so as to be exposed to light ; a 

 temperature suiting vegetation is also to be given. Ani- 

 malcules may appear in great numbers ; they are an indi- 

 cation of nitrogenous matter, and one proof of the presence 

 of substances capable of putrefaction. It may be that 



