These calculations were based on normal adult 

 female Single Comb White Leghorn chickens. 

 It is evident, thei-efore, that the desirable number 

 of birds to be used in an experimental group is 

 determined by the blood component that is of 

 particular concern to the problem at hand. 

 Fewer birds would be needed in each group if 

 red-cell counts were of chief concern than if 

 eosinophils were to be followed critically. The 

 high variability for some of the blood com- 

 ponents makes it necessary for practical reasons 

 to accept high coefficients of variability in order 

 that the number of birds involved in each experi- 

 mental group can be small enough to make the 

 experiment practical. 



Another problem studied by Lucas and Den- 

 ington (unpublished data) has been the number 

 of cells that should be tabulated from a slide 

 when making a differential count. The accuracy 

 increases by the square root of the multiples of 

 100 cells counted. In other words, 400 cells 

 give values that are twice as accurate as when 

 100 cells are counted, and 900 cells give values 

 three times as accurate as when 100 cells are 

 counted. 



The question arises, When is the point of di- 

 minishing returns in accuracy reached for the 

 time spent in making the counts? In the studies 

 made by Lucas and Denington, it was found that 

 100 cells were sufficient for lymphocytes and 

 heterophils; but for monocytes, eosinophils, and 

 basophils, 292 cells were needed to give the 

 maximum accuracy for the time spent in making 

 the counts. In making the counts, 300 cells 

 were used. Lucas and Denington found also 

 that the number of birds used in an experiment 

 can be reduced if the number of cells counted 

 per bird is increased. The gain comes chiefly in 

 those blood components having high variability — 

 especially so when the variability within birds 

 is as great as the variability between birds. 



In the same experiment there were males from 

 the same source and they were killed at about 

 550 days of age. Thirty-three individuals went 

 into the averages presented in table 17. Labora- 

 tory males showed higher values than Laboratory 

 females for number of erythrocytes, grams of 

 hemoglobin, and volume of packed cells (hema- 

 tocrit percentage). The total white-cell count 

 was lower for males than for females. The sexes 

 did not differ widely in the percentage values 

 for monocytes, eosinophils, and basophils. Fe- 



male chickens showed a higher percentage value 

 for lymphocytes than did male chickens. The 

 reverse was true for heterophils. 



A higher erythrocyte number for adult males 

 than for adult females agrees with the work of 

 Juhn and Domm ( 1930) . Before maturity there 

 was no difference between the sexes. The aver- 

 age values given for males of 3,600,000 and for 

 females of 2,700,000 given by Taber et al. 

 (1943) agree fairly well with those given in table 

 17. The averages computed from Kitaeva's data 

 (1939) for adult birds were 3.40 million eryth- 

 rocytes per mm.^ for males and 2.92 million 

 per mm.^ for females. Domm and Taber (1946) 

 obtained an average erythrocyte count for males 

 of 3,250,000 and for females of 2,610,000. 

 They sought to determine if a diurnal rhythm for 

 erythrocytes in the circulating blood existed in 

 chickens, comparable to that which had been 

 found in some mammals. They took their 

 samples at noon, 6 p. m., midnight, and 6 a. m. 

 They found a definite tendency in males to give 

 highest values at midnight and lowest at noon. 

 The same tendencies were evident in females 

 also, but the difference in averages at these two 

 times of the day was not as great in females as 

 in males. Domm and Taber found a seasonal 

 variation in erythrocyte counts; the lowest counts 

 came at the period of highest reproductive ac- 

 tivity and the highest counts at the time of lowest 

 activity. See also Domm, et al. (1943). 



Kakara and Kawasima (1939) found that 

 birds sitting on eggs had a lower red-cell count, 

 lower thrombocyte count, and lower total white 

 cells than did laying hens. 



Chickens moved to a high altitude, 6,000 feet, 

 showed a slight increase in hemoglobin and eryth- 

 rocyte count, according to Vezzani (1939). 



An extensive study of erythrocyte numbers for 

 many species of birds was made by Nice et al. 

 (1935). Counts on wild birds ranged from 

 3,930,000 (tufted titmouse) to 7,645,000 

 (junco). The median count was 5,230,000. All 

 of the counts are higher than the average for 

 chickens. In the bobwhite, a gallinaceous bird, 

 the average was 3,532,000. Erythrocyte counts 

 and hemoglobin determinations on pigeons and 

 on doves by Riddle and Braucher (1934) gave 

 higher values for males than for females. They 

 observed seasonal differences also, with the high- 

 est values occurring in the autumn and lowest 

 values in the summer. 



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