PEOGRESS IN BIOLOGICAL INQUIRIES, 19 30 625 



noncommercial species was very evident in all sections of the river 

 studied. Paper shells and floaters, worthless species as far as button 

 manufacturers are concerned, were the only species found to be re- 

 placing themselves under the new conditions. Young of the com- 

 mercial species were rarely found, while large numbers of the young 

 floaters and paper shells were collected in many places, particularly 

 behind wing dams, log-jams, and other obstructions where the sand 

 shells and other valuable species had been killed out by the silt 

 deposits. 



POLLUTION STUDIES 



In connection with the Mississippi Kiver survey, the glochidia 

 studies, and certain industrial problems, the effects of stream pollu- 

 tion on fish, fish food, and fresh-water mussels have been investigated 

 both in the field and in the laboratory. Throughout the summer and 

 fall the bacteriologist of the unit has followed the bacterial flora in 

 all of these studies, and the chemical, physiological, and bacteriologi- 

 cal aspects have been investigated by other members of the staff. 

 Work has been carried on and is in progress along the following 

 lines : 



(a) General and municipal sewage pollution; (6) industrial pol- 

 lution, particularly sulphur, acid pollution, and arsenic; (c) erosion 

 silt; and {d) oxygen saturation. 



In the experimental studies on pollution the oxygen limits as in- 

 fluenced by these various pollution factors have been given particu- 

 lar attention. Fresh-water mussels, for example, show a marked re- 

 duction in their vital activities when the oxygen saturation is reduced 

 to below 25 per cent, and their reactions to the specific substances 

 polluting the water are modified by the state of activity as produced 

 by the oxygen saturation, thus creating a physiological vicious cycle. 



BOTTOM STUDIES 



Experimental studies both in the laboratory and on selected areas 

 in the river concerning the physiological, chemical, and biological 

 factors contributing to the survival or elimination of juvenile mus- 

 sels have been made with a view to obtaining data on suitable grounds 

 for the planting of young mussels. Much progress has been made 

 in this field where there are few previous observations. 



HOLDING AND FEEDING OF ADULT FRESH-WATER MUSSELS 



In view of the rapid decline in the valuable commercial mussels in 

 so many parts of the Mississippi drainage and the attendant diffi- 

 culties in securing adequate breeding stock and good glochidia for 

 the propagation work, series of adult mussels have been held 

 throughout the year in tank aquaria to determine whether it is 

 feasible to hold adult mussels in numbers and thus select proper 

 breeding stock. As a corollary of this work the conditions of the 

 animals as shown by blood and other biochemical studies have been 

 followed. One of these biochemical studies has demonstrated that 

 mussels in good condition when first taken from the river have a 

 large reserve of stored food in the form of glycogen, and that if kept 

 in water containing practically no mussel food this reserve of gly- 

 cogen is steadily used up. 



