426 AMOUNT OF A BIOLOGICAL SAMPLE 



/5.30\ 

 \5A7) _ 



^'"'"'•^n^fP — - = (238 =. 8.6) 103 cells/Ml. 

 0.066 



(2) In the case of two different types of cells in the same section: 



Epithelial cells comprise 25% of the area of a section. 



Neck chief cells comprise 75% of the area of the section. 



Epithehal cell count = 262 ± 6.7. 



Epithelial cells per counting area = (262 ± 6.7) 0.71 = 186 ± 4.8. 



/5.00\ 



aS6 =^ 4.8(85^) {5 A7) ^ ^.25 = (55 =. 0.14) 10^ epithelial cells/^l 

 0.066 



Neck chief cell count = 326 ± 8.5. 



Neck chief cell per counting area = (326 ± 8.5) 0.71 = 232 ± 6.0. 



/5.00\ 

 (232 ± 6.0) (85.7) \5.47/ ^ q ^^ ^ ^206 ± 5.3) 10« neck chief cells//xl. 



The determination of a constituent in each type of cell in this section may 

 follow the example given: 



From the nearest section containing onl.v epithelial cells a peptidase activity 

 of 0.125 X 10'^ units per cell was found. Therefore, the activity arising from the 

 epithelial cells was: 



(55 ± 0.14) 10=" X (0.125) 10"^ = 6.8 units/Ml. 

 and 



(6.8) (0.066) = 0.45 unit/section. 



The activity of the section composed of both the epithelial and neck chief 

 cells was found to be 1.70 units, of which 0.45 unit was ascribed to the epithe- 

 lial cells present. Therefore, the activity of the neck chief cells in the section 

 was considered 1.70 — 0.45 = 1.25 units, and the activity of these cells was 

 1.25/0.066 = 19 units/yul., or 19/206 X lO' = 0.092 X lO"" units/neck chief cell. 



Nitrogen. The total nitrogen in a sample has often been used 

 as an indication of the quantity of protoplasm present. Measure- 

 ments of the nitrogen content may be carried out by one of the pro- 

 cedures given on pages 230-239, and 283. 



Nucleic Acid. Berenblum, Chain, and Heatley (1939) employed 

 the estimation of nucleic acid phosphorus as an indication of the 

 quantity of cellular material present, in an attempt to refer meas- 

 urements to the amount of metabolizing substance rather than to 



