The toxicological control of the second variety is assayed by pouring 

 the water to be tested into 10 beakers, 100 ml in each. Clean water in 

 the same quantity serves as a control. To each of the beakers one-two 

 day oldVaphvua magna are added. The duration of the experiment is 30 

 days at a temperature of 17-22 °C. The Vaphnia are fed with ChlonnlZa &p . 

 and the water is changed every 3-4 days. The criteria of toxicity in- 

 clude survival, rate of reproduction (fecundity), time of maturation, and 

 frequency of moulting. 



The toxicity or harmfulness of the water for the organism is expressed 

 by three degrees: 



1. First Degree. Water is toxic. 50 percent or less of 

 the Vaphnia live less than 30 days. 



2. Second Degree. Water is harmful. 80 percent or more 

 of the Vaphnia survive for 30 days, but fecundity is 

 reduced by 25 percent or more as compared with control 

 populations. 



3. Third Degree. Water is clean. All the Vaphnia. survive, 

 and the fecundity is not reduced by more than 25 percent 

 in comparison with the control. 



By simultaneously conducting toxicologic control of the first variety 

 every 5-7 days while running the longer experiment of the second variety, 

 the occurance of late results is minimized. Compensation is achieved by 

 exerting simultaneous control of the discharge water and the receiving 

 water of the water body. If periodic discharge occurs, detection is en- 

 abled by the toxicological control of the first variety. 



Toxicological control does not indicate the nature of the toxicant, 

 but does show the danger of the water in question for many aquatic or- 

 ganisms. 



10 



