572 Prof. Woodhead, The remits of 



this method of sterilisation is admirably suited for the treatment 

 of the Cambridge water and indeed of all waters where the 

 amount of organic matter is small but which are open to suspicion 

 on other grounds. Even in those chalk waters in which the 

 amount of organic matter is variable this method may be utilised, 

 though in cases where the amount of decomposing organic matter 

 is greater the difficulty of getting rid of taste and smell may be 

 increased and some modification of the process may have to be 

 devised. 



It may be asked what is the effect of this treatment on living 

 animal organisms. Sometime ago F. S. Locke* following up ex- 

 periments carried out by Naegeli and by Ringer and Phearf found 

 that very minute quantities of copper dissolved in distilled water 

 had a toxic effect on tadpoles, killing them in from two to twenty- 

 two hours, one part of sulphate of copper in two millions of water 

 proving fatal. It was noted that several other heavy metals acted 

 in the same way. Naegeli had already pointed out that one part 

 of copper in seventy-seven million parts of distilled water was 

 fatal to S'pirogyra. Chlorine in the minute quantities used in 

 the experiments above recorded seems to act equally powerfully 

 on vegetable protoplasm, but on the health of tadpoles one part of 

 chlorine in two million parts of tap-water has absolutely no effect, 

 the tadpoles remaining exceedingly lively at the end of nine or 

 ten days. Further it was noted that chlorine added to distilled 

 water actually neutralises the action of copper, iron, and tin. It 

 does not prevent the formation of a carbonate of lead, and tadpoles 

 kept in chlorinated distilled water in which has been placed a 

 bright strip of one of these metals remained active and vigorous 

 whilst tadpoles that are placed in distilled, but non-chlorinated, 

 water in which are placed similar strips of metal soon die. It is 

 interesting to note that water drawn from the laboratory tap 

 which has remained in the pipes for some little time proved fatal 

 to tadpoles in 24 hours, showing that these creatures are very 

 susceptible to slight changes in the water in which they are 

 placed. Water drawn directly from the main and which has not 

 remained in the pipes for any length of time has no effect upon 

 the tadpole, which remains perfectly lively just as it remains in 

 any dilution of chlorine up to one part in two millions of water 

 whether bright metal has been added or not. This chlorinated 

 water therefore is less deleterious to tadpoles than is water that 

 has passed through the laboratory supply pipe, water that we 

 constantly drink and use for all ordinary purposes. 



It is evident then that in the Cambridge water very minute 

 quantities of the oxy-chlorine compound are sufficient to bring 



* Journ. of Physiol. London, Vol. xviii, 1895, p. 319. 

 t Journ. of Physiol. London, Vol. xvii, 1894-5, p. 423. 



