BACTERIOLOGY OF THE OYSTER. y 



where a third set of cilia located on the very edge of the gill conveys 

 the entangled organisms on the mouth. The arrangement of these 

 last two sets of cilia can be seen in the plate. In this diagram 

 the bent arrows show the course of the water through the gills into 

 the cloacal chamber. The straight arrows indicate the course of the 

 mucus and the entangled micro-organisms to the mouth. 



When the valves of the oyster are open the current induced by the 

 cilia is carried out of the oyster between the points "A" and "B." 

 When the valves of the oyster are closed, however, the cilia keep 

 waving as vigorously as before, because the oyster has no control over 

 their movement, but in this case the current cannot pass out between 

 the valves and we have what might be called a closed circulation. 

 Instead of going out between the points ''A" and "B," as is the case 

 when the valves are open, the current must neccessarily return to the 

 gill chamber around point "A," for a study of the currents induced by 

 the cilia and taking the direction indicated by the arrows shows that no 

 other course is possible. All the cilia of the cloacal chamber direct 

 their motion towards point "A" and "B." All the currents in the 

 branchial chamber are either through the gills into the cloacal chamber 

 or along the edge of the gills to the mouth. As water is driven through 

 the gills to the cloacal chamber water from the cloacal chamber must 

 necessarily take its place. As point '' A " is the point of least resistance 

 the water necessarily passes from the cloacal chamber to the gill 

 chamber around that point and further not only is there nothing to 

 obstruct this current, but the current induced by the cilia on the edge 

 of the gills is such that it would draw the water from the cloacal 

 chamber into the gill chamber around this point. Hence we see that 

 in the oyster we have a complete cycle of currents induced by ciliary 

 motion. The result is that all the water in the oyster is filtered 

 through the gills many times in an hour and the process is repeated 

 every few minutes. 



It happens that when bacteria enter the gill or branchial chamber, 

 two courses are open. They may follow the currents through the 

 gills into the cloacal chamber or they may become entangled in the 

 mucus of the gills and be conveyed along the edge of the gills to the 

 mouth. The chances of a bacterium going in either of these courses 

 are about equal and if many bacteria are present some may go by one 

 course and some by the other. 



! A study of table No. 1 will show that the B. prodigiosus followed 

 both of these courses, some were entangled in the mucus and were 



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