Normal Blood
In considering what may be termed normal blood, it must be borne in mind that the normal varies for men, women, and children:
| Hb. | Red Cells | Leucocytes | ||
| Men, | 90 to 110%, | 5 to 5½ | million, | 7500. |
| Women, | 80 to 100%, | 4½ to 5 | million, | 7500. |
| Children, | 70 to 80%, | 4½ to 5 | million, | 9000. |
Color Index
This is obtained by dividing the percentage of the haemoglobin by the percentage of red cells, 5,000,000 red cells being considered as 100%.
To obtain the percentage of red cells it is only necessary to multiply the two extreme figures to the left by two. Thus if a count showed the presence of 1,700,000 red cells the percentage would be 34 (17 × 2 = 34). If the Hb. percentage in this case were 50, then the color index would be 50 ÷ 34, or 1.4.
In normal blood the color index is, approximately, 1.
In anaemias we have three types of color index: 1. The pernicious anaemia type which is above 1. Here we have a greater reduction in red cells than we have of the haemoglobin content of each cell. For example, in a case of pernicious anaemia we have 2,000,000 red cells (40%) and 60% of haemoglobin, 60 ÷ 40 = 1.5. 2. The normal type, when both red cells and haemoglobin are proportionally decreased, as in anaemia fallowing haemorrhage. 3. The chlorotic type. Here there is a great decrease in haemoglobin percentage, but only a moderate decrease in the number of red cells. Hence the color index is only a fraction of 1. For example, in a case of chlorosis we have 40% of haemoglobin and 4,000,000 red cells, 40 ÷ 80 = 0.5.
One can judge fairly well the approximate color index by noting the character of the staining of the red cells. This is faint in bloods of low color index and deeper than normal in cells in a case with high color index.