194 Report of the Board of Shell Fish Commissioners 



made of the locality, date, depth, kind of bottom, density and 

 condition of the sample. To the sample 20 cubic centimeters of 

 formalin is added to prevent the decay or further growth of the 

 organisms contained. It is then allowed to stand for twenty- 

 four hours or more to settle. 



The cup used to collect specimens of water is so constructed 

 that it remains closed until it rests upon the bottom. The water 

 flows in at the valve in the top which stands at a level one foot 

 above the bottom. It would be more satisfactory could the 

 sample be collected nearer the bottom than one foot, but experi- 

 ence has shown that when collected at a lower level a consider- 

 able quantity of sediment, stirred up by the contact of the cup 

 with the bottom, is included, and this interferes- with the exami- 

 nation of the specimen. 



When the organisms contained in a sample have settled to 

 the bottom of the flask the clear water above is siphoned away 

 and the residue, usually amounting to about 200 c. c., is emptied 

 into a smaller flask, Figure 11. This is again allowed to settle 

 and the clear water is siphoned away, reducing the residue to a 

 volume equal to about 20 c. c., which is placed in a small bottle, 

 Figure 11, properly labeled and filed. The food material in the 

 sample is thus concentrated to a bulk convenient for examina- 

 tion. 



A specimen when examined microscopically is first reduced in 

 quantity to exactly 20 cubic centimeters. After thoroughly 

 shaking the specimen one cubic centimeter is removed, before 

 it has time to settle, with a graduated pipette and placed in a 

 "Rafter Cell," Figure 11. 



A Kafter Cell is an apparatus holding one cubic centimeter of 

 liquid, so made that the liquid is spread over a surface of 1,000 

 square millimeters to a thickness of one millimeter. With this 

 apparatus it is possible to count the actual number of organ- 

 isms in an accurately measured part of a cubic centimeter of 

 water. Such counts from two or more cubic centimeters of 

 each specimen are made and used as a basis for estimating the 

 total quantity of food organisms in the entire specimen. 



From the examinations made thus far the number of organ- 

 isms available to oysters as food over the natural bars in Anne 

 Arundel County, is calculated to be from 20,000 to 100,000 per 



