64 PEARLS AND PEARLING 



paper. The sawdust and waste is thrown into the streams 

 and farther down where the water is rather quiet, the 

 impure refuse settles to the bottom and is very destruc- 

 tive to the mussels. 



In some of the streams of the Southern States the 

 water contains a large amount of carbonic acid, which is 

 very injurious to the mussels. It is very probable that 

 the conchiolin epidermis is developed to protect the shell 

 from the effects of acids. Where the epidermis is badly 

 worn or broken off, as is often the case at the umboes 

 or beaks of the shells of old mussels, the acid has an 

 opportunity to eat into the shell and sometimes eats 

 through the heavy portion of the shell and causes the 

 death of the animal. 



Another thing that is detrimental to mussels is the cus- 

 tom of cutting timber for various economic uses. While 

 the timber remains standing, the water does not leave the 

 soil rapidly and the brooks and creeks have many deep 

 places where there is always plenty of water and the 

 mussels thrive in such places. After the timber is cut, 

 the rain water runs off rapidly and the streams become 

 so dry that mussels cannot live in them. 



The* most dangerous enemy of the mussel has been 

 man. His increasing activities in gathering shells and in 

 pearl hunting have so depleted many rivers that it will 

 require considerable time to replace the loss. Although 

 man has been the enemy of 'the mussels, he is now becom- 

 ing their friend, for he is learning and using methods 

 which greatly assist in preserving their lives and increas- 

 ing their numbers. 



