382 



luted waters. The reactions of fishes to the results of contamination 

 with natural organic matter, such as decomposing bodies of plants 

 and animals, are generally advantageous, as the fish turn away from 

 the polluted area. The result of this investigation shows that in the 

 case of gas wastes the reactions are usually disadvantageous, — the 

 fishes swim into the polluting substances without recognizing them or 

 turning back from them even when their toxicity is such as t(^ cause 

 death within a short period. The detrimental character of gas wastes 

 is thus increased many fold. 



The toxicity of waste differs for different species of fish and is 

 greatest for the more valuable fishes as indicated by Dr. Wells' wf)rk 

 (Article VII of this volume). It will be shown to be generally greater 

 for the smaller and younger fishes. The w-riter's investigations will 

 show that this rule holds good down to the youngest fry studied. 

 Sollmann ('06) found some evidence that the eggs and newly hatched 

 embryos of marine Pundulus are more resistant to poisons than the 

 adults. He however seems to question his results in this respect 

 because of the long exposure in the poison solutions and small quan- 

 tity of the solution in proportion to the size and total oxygen demand 

 and excretory output of the adult fish. Child's work with phenyl 

 urethane which was done after long experience in the use of such 

 poisons showed that in marine Fimdulus the resistance declined rapid- 

 ly from a maximum in the two-cell stage of the egg, to the time of 

 hatching. In Tautogolobris the resistance fell from a survival time of 

 675 minutes soon after fertilization to 15 minutes at the time the heart 

 began to beat and rose to 20 minutes at the time of hatching, when 

 the experiments were discontinued. The resistance of the eggs and 

 embryos of fresh water fishes has not been studied and compared with 

 that of the adults, but there is every evidence that the rule reported 

 here will hold good throughout the age and size series beginning about 

 the time of hatching. The most sensitive period must be determined 

 before the minimum fatal quantity can be established with any cer- 

 tainty. For this reason no attempt has herein been made to determine 

 the minimum which will prove fatal to the fishes studied. Dr. Wells 

 has found that the resistance of some fishes to various factors varies 

 greatly with the time of year. The lowest point comes between the 

 middle of June and the last of July when such fishes as the cyj)rinids 

 can hardly be taken from the w^ater before death sets in. From this 

 time the resistance slowly rises until September. Then the rise be- 

 comes more rapid and reaches its highest point in March and April, 

 when all the fishes are exceedinglv resistant. With the onset of the 

 breeding season the resistance falls, though whether or not it con- 



