tions might lead to the disturbance of the physiological normal level of 

 the organism and its biological well-being (3). Such an attitude is quite 

 natural for a physiologist, since from the physiological point of view, any 

 one of the numerous functional systems is equivalent and indispensable for 

 the normal activity of the whole organism, and the persistant disturbance 

 of each of them will inevitably destroy the activity of the others, in- 

 cluding the reproductive function. 



According to this point of view, we have formulated ideas on toxicity 

 criteria in water toxicology. We must consider as toxic (threshold) a con- 

 centration which evokes some expressed pathological change in any of the 

 functional systems of an individual organism, since persistant disturbance 

 of the activity of any physiological system, whether it be blood circulation 

 or hemopiesis, respiration or nutrition, behavior or reproduction, sooner 

 or later leads to irreversible homeostatic disturbances and finally to the 

 destruction of organisms. 



It appears from the above that the threshold concentration value deter- 

 mined from fish toxicological investigations to develop criteria, depend 

 largely on how correctly we identify the function affected, i .e. , the ade- 

 quacy of methods for estimating pathological changes in the activity of the 

 functional system. Therefore, the search for more sensitive, specific 

 methods with high resolution which permit us in a very short time to obtain 

 scientifically substantiated MPCs for harmful substances, is of primary 

 importance. Already MPC values for almost a thousand various substances 

 discharged into water used for fisheries are needed. 



The solution of this colossal problem in a very short time is possible 

 only with the aid of more sensitive contemporary physiological and biochemi- 

 cal methods for monitoring the functional state of test fish and other 

 aquatic organisms. These methods surpass 10-100 times the "fish trial-and- 

 error method" due to their resolution capabilities. The selection of the 

 specific method to determine the MPC value of any harmful substance must be 

 based on the knowledge of toxicodynamics of the substance under investiga- 

 tion and the understanding of the effect of various toxin groups, i.e., a 

 clear identification of the most sensitive target function. Here is an 

 example to explain this thesis. 



For example, a large group of substances of an organic nature (toxins 

 of the phenol series, many pesticides, dyes, etc.) cause a complicated 

 symptom-complex of intoxication in fish. This permits us to assume the in- 

 fluence of these substances is on the central nervous system. However, 

 this required direct experimental proof and it was obtained (4, 3, 19-21) 

 using the model of phenol intoxication in fish. In a number of experiments 

 beginning in 1962-63 at the USSR Academy of Sciences Institute for Biology 

 of Inland Waters, the dominant role of the central nervous system in the 

 development of the complicated symptom-complex of intoxication in fish with 

 toxins of the phenol series has been proven. For example, we succeeded in 

 completely cutting off the first phase of phenol intoxication--rapid motor 

 activity--in anesthetized crucians (novocain, urethane). In other words, 

 generalized inhibition of the central nervous system, resulting from narco- 



49 



