824 KEPORT OF COMMISSIONEE OF FISH AND FISHERIES. [lOJ 



The principal obstacle lu the way of attaining this end is the pollu- 

 tion of the water in the small streams which are not suitable for navi- 

 gation or rafting, which are corrupted by solid or liquid substances 

 thrown into the water by various manufactures, and which are hurtful 

 to the reproduction and existence of fish. 



The Academy appeals to science to aid in the accomplishment of the 

 objects had in view by the authorities. Accepting the proposition of 

 one of its members, who has generously placed at its disposal the sum 

 of three thousand francs, it requests that a thorough study should be 

 made of the following questions, both chemical and biological: 



(1.) Which are the special substances in the principal industries which 

 when mingling with the water of small streams render them incom- 

 jjatible with the existence of fish and unfit for the use of man and 

 beast. 



(2.) Prepare a list of the Belgian rivers which have become depopu- 

 lated from this cause, indicating the industries peculiar to each of the 

 rivers, and give a list of the food-fish which used to live in these rivers 

 before the establishment of the manufactures. 



(3.) Indicate practical means for purifying the water before it leaves 

 the manufactories, so as to render it fit for fish to live in, without en- 

 dangering the industries, by combining the aids afforded by the con- 

 struction of clearing-basins, by filtering, and by the employment of 

 cliemical agents. 



(4.) Make special experiments relative to the substances which in each 

 industry cause the death of fish; and also relative to the degree of re- 

 sistance which each kind of food fish can offer to its destruction by the 

 causes above mentioned. 



The treatises must be written legibly, and should be addressed, pre- 

 paid, to M. Liagre, permanent secretary, at the Palace of the Academy, 

 not later than October 1, 1884. The Academy requests that all quota- 

 tions should be exact. Authors will, therefore, indicate the edition and 

 the pages from the works quoted. Illustrations will only be admitted 

 when drawn by hand. Authors will not sign their name to their treatise, 

 but will simply sign by some mark, which they will reproduce in a 

 note containing their name and address. Failure to comply with this 

 formality will prevent a person from obtaining the prize. Treatises 

 sent in after the above-mentioned date, or those whose authors make 

 themselves known in any way whatever, will be excluded from the com- 

 petition. 



The Academy deems it proper to call the attention of authors send- 

 ing in treatises to the circumstance that from the time when such 

 treatises are submitted to the Academy they are and will remain de- 

 posited in its archives. Authors, however, can have copies of their 

 treatises made, at their own expense, by addressing tlieir request to the 

 permanent secretary. 



