434 AMOUNT OF A BIOLOGICAL SAMPLE 



12. Empty the dye soln. plus amoeba into a small reaction tube 

 containing a measured vol. water (100 fA.). Rinse the capillary with 

 the water and stir the soln. by means of a magnetic "flea" (page 

 179). Use a permanent magnet, rather than the periodic electromag- 

 net, to stir carefully to avoid damage to the organism. 



13. Remove the "flea" with the magnet, and the object with a 

 braking pipette. 



14. Transfer the diluted dye soln. to a cuvette and obtain its 

 colorimeter reading using a yellow filter (S57 with the Zeiss step 

 photometer) . 



15. Run an empirical set of standards with different lengths of 

 dye columns in the capillary and plot a curve of the colorimeter 

 readings against the lengths of the dye columns. The standard curve 

 may be used as long as neither the capillary nor dye soln. is changed. 

 To check the constancy of the dye soln., run one or two samples of 

 dye alone, which have known lengths in the capillary, in each ex- 

 periment. 



16. Calculate the vol. of the object (V) by the formula: 



V = A{Lt-L) 



where ^4 is the cross-sectional area of the capillary, Lt the length of 

 the dye plus object in the capillary, and L the length of the dye 

 alone. The value of L, corresponding to the colorimeter reading of the 

 unknown, is obtained from the standard curve. 



