424 AMOUNT OF A BIOLOGICAL SAMPLE 



\ 



ting circular sections of a known thickness and diameter as de- 

 scribed on page 427. 



Numbers of Cells. When the cells are in suspension their 

 number may be determined by counting in a hemocytometer cham- 

 ber. It may aid in the counting to stain the cells first. However, the 

 measurement of the number of cells in histological preparations is 

 more involved. A technique for cell counting in mounted stained 

 sections of tissue was described by Linderstr0m-Lang, Holter, and 

 S0eborg Ohlsen (1934). 



The data of Rask-Nielsen (1944) for the number of cells per unit 

 volume of pyloric mucosa may be taken to illustrate the counting 

 technique. A microscope magnification of 300 X was used, and the 

 ocular was equipped with an ocular micrometer containing a circle, 

 divided into quadrants, which enclosed an area corresponding to 

 0.0638 mm.^ of the tissue section. Six to ten random counts, uni- 

 formly distributed over the stained section, were made of all nuclei 

 and fragments thereof within the bounds of the counting area. 



In a given case a mean of the chief cells from eight random counts 

 was 229. The mean error of the mean value of the counts was ±4.4, 

 obtained from the formula: 



rj^ / q-a 



where ( SA^) is the sum of the squares of the individual deviations 

 from the mean value, q the number of counts, a the counting area, 

 and A the area of the section. 



In order to convert the number of nuclei plus fragments per count- 

 ing area (229 ± 4.4) to cells per counting area, a correction factor 

 for the fragments must be applied. This factor is 12/(12 -\- h) 

 where 12 is the thickness of the section and h the height of the 

 nuclei, both expressed in microns. In this case the factor equals 

 0.71; hence: 



(229 ± 4.4) 0.71 = 163 =>= 3.1 cells/counting area 



Since the sections were cut from a cylinder of fresh-frozen tissue having a 

 diameter of 2.64 mm.: 



2 (2.64)2 = 547 mm.2, area of a fresh section 



6.47 X 0.012 = 0.066 /xl, volume of a fresh section 



5 47 

 and - '„-„ = 85.7 counting areas/fresh section 



U.Ubdo 



