8 BACTERIOLOGY OF THE OYSTER. 



From this table it can be seen that B. prodigiosus was isolated from 

 all the holes in oyster No. 1 at the end of ten minutes and in oyster 

 No. 2 at the end of four minutes. It is further seen that in oyster 

 No. 1 B. prodigiosus appeared first at hole No. 1, two minutes 

 later at hole No. 5, and after another interval of tw:o minutes 

 at hole No. 4. In oyster No. 2 the bacillus appeared first at 

 hole No. 1 and two minutes later at holes Nos. 5 and 4. In neither 

 case did B. prodigiosus appear at holes 5 or 4 before it appeared at hole 

 No. 1, nor in either case at hole No. 4 before hole No. 5. 



To understand the reason for these results a description of the 

 ciliar}^ mechanism of the oyster is necessary. 



When one opens an oyster without mutilating it, there is found 

 between the two flaps of the mantle four folds of tissue which are the 

 gills. These folds appear solid, but are really flaps folded back upon 

 themselves and attached by the edges to the body so that really each 

 gill is V shaped in cross section and the four gills form a double W 

 (WW). With the unaided eye it can be seen that there are flne stria- 

 tions running verticallj^ across each gill. These are the gill filaments. 

 If we examine these filaments with a microscope we will see innumera- 

 able hairs or cilia about 1 -500th of an inch long or less, waving vigor- 

 ously back and forth. If we examine the cilia closely we find that 

 they lash vigorously in one direction, recover themselves slowly and 

 repeat the vigorous stroke. The movement is quite comparable 

 to a man rowing a boat. He pulls vigorously in one direction, 

 recovers himself and repeats the stroke. Now if we consider the boat 

 fastened so that it could not move, the oarsman's efforts would send 

 the water past the boat instead of propelling the boat through the 

 water. Here w^e have the exact condition in the oyster. As Brooks 

 (The Oj^ster, 1906) says, these little hairs "set up a current in the 

 water. Each one is so small that its individual effect is inconceivably 

 minute, but the innumerable multitude causes a vigorous circulation 

 and each one is set at such a position that it drives the water before 

 it from the gill chamber into one of the water pores and so into one 

 of the water tubes inside the gill. As these are filled they overflow 

 into the cloacal chamber and fill that." This set of cilia are located 

 on the edges of the filaments and force the water through the gills 

 from the branchial into the cloacal chamber. There is another set 

 of cilia which wave in the opposite direction and by means of the 

 mucus which is secreted by the mucus cells, they collect and entangle 

 the micro-organisms and carry them over to the free edge of the gill 



