PROTECTION FROM TOXIC REAGENTS 213 



attacked the problem of the toxicity of metallic salts on fishes on 

 account of her interest in stream pollution. Using lead nitrate, she 

 found that the fatality curve is described by the equation K = i/t log 

 i/conc, where iT is a constant dependent upon the toxic substance 

 employed and / is survival time for any given concentration (cone). 



When a number of minnows (Leuciscus) were killed successively 

 by placing them in the same 500 cc. solution of N/'io lead nitrate, the 

 survival time was found to be prolonged with each successive fish 

 until the eighth had a survival time approximately double the stand- 

 ard figure for that concentration and size of fish. The actual sur- 

 vival times reported are, in order, 73, 89, 92, 93, 94, 120, and 130 

 minutes. Carpenter makes the deduction that the solution was 

 successively weakened by the abstraction from it of a certain pro- 

 portion of the lethal substance by each fish tested and that the 

 lethal efficacy was thus progressively reduced. 



The lethal efficacy of the solution varied in inverse proportion to 

 the actual size of the fish exposed and directly according to the 

 amount of lead (as Pb) required to kill the fishes. If the original solu- 

 tion be relatively weak, a single fish will remove an important frac- 

 tion from a small amount of solution, and will therefore show a 

 longer survival time than a similar fish isolated into a large volume 

 of solution of similar strength. This is in keeping with Huxley's ob- 

 servations (1922) on the action of mercuric chloride on the gill tissue 

 of Mytilus. Carpenter concluded that the lead salt causes death, 

 due to the formation of a film over the gills and skin of the fish, by 

 an interaction of mucus and the metallic ion, which causes death by 

 suffocation. If insufficient lead ions are present, the film is shed; and 

 the solution being thus freed from its toxic element, recovery en- 

 sues. 



An attempt was made to establish the amount of lead which en- 

 ters into combination with the mucus, and the amount, if any, 

 which enters the blood-stream. Two large minnows were placed 

 together in 1-5 liters of distilled water, to which was added sufficient 

 lead nitrate to supply 6.21 mg. of lead. Immediately after death, 

 the bodies were transferred to fairly dilute acetic acid for 4 minutes 

 until the gills were quite clear. After washing the bodies in distilled 



