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The literature provides all the data needed to calculate the ratio between the amount of haemoglobin and the total surface area of erythrocytes in 54 species of mammals ranging in body mass from 2.5 g to more than 1000 kg. Analysis shows that the concentration of haemoglobin (Hb; g%) does not defend on the body mass ofthe mammals studied. The number of erythrocytes in 1 mm of blood (RBC; 10 x mm ) is significantly lower, and the diameter of these cells significantly higher, among larger mammals as opposed to smaller ones. The result is that the total surface area of erythrocytes in 1 mm of blood (TSAE; mm x mm ) is significantly lower among larger mammals, while the Hb/TSAE ratio (pg x ^m- ) is significantly greater. These results point to the smaller size of erythrocytes of smaller mammals permitting much greater numbers to exist, thereby producing a greater TSAE and smaller Hb/TSAE ratio. The greater total surface area of red blood cells per unit volume of blood in small mammals can in turn be presumed to allow for full saturation of haemoglobin by oxygen, even where the period of contact between erythrocytes and air in the lungs is shorter than in their larger counterparts.
The nestling development of the studied House Martins lasted 20 days. During the first 5-6 days and the last 4-5 days of the development the concentration of haemoglobin increased, while the size of the total surface area of erythrocytes in 1 mm³ of blood increased respectively, manifesting well-fitting. As a result the amount of the haemoglobin functioning on a unit of red cell's surface remained constant. The number of erythrocytes in 1 mm³ of blood increased so significantly, that even despite simultaneous decrease in their size in the last days of the nestlings' development, it causes the increase in the value of haematocrit. Thus the general mechanism forming the respiratory function of a blood volume unit is the same as in other altricial birds. Between the 5th-6th days and the 15th-16th the values of red blood indices did not change. Such a phenomenon did not occur in other studied passerine birds.
Data from 75 bird species weighing between 6 g and > 16 kg confirmed a supposition that the amount of haemoglobin per unit surface area of erythrocyte was not dependent on body mass. It showed a constancy across the range reflecting adjustment of the total surface area of erythrocytes in relation to blood haemoglobin concentration. This conclusion is based on an inverse correlation between the numbers and sizes of red blood cells.
The haemoglobin concentration and the total surface area of erythrocytes in the unit of blood volume decreased with similar intensity with the increase of body mass in 23 species of studied birds, weighing from 6 g to 170 g. Hence the amount of Hb per unit of the erythrocyte surface did not depend on the body mass of birds. Species of a greater body mass had smaller total surface area of erythrocytes in 1 mm³ of blood, as they had a smaller number of larger red blood cells. The changes in number and size of erythrocytes with the increase of the body mass occurred in such a way that, as a result, the value of haematocrit remained statistically the same in the studied birds.
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