This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
The Bed Corpuscles Of Human Blood (Fig. 53) are circular disks a little hollowed out on each face. Seen singly with a microscope each is not red but pale yellow; it is only when they are crowded in a heap that the mass looks red; a drop of blood spread out very thin on glass, or mixed with a tablespoonful of water, is pale yellow and not red. Soon after blood is drawn most of the red corpuscles cohere side by side in rows, something like piles of coin.
The red corpuscles of most mammalia resemble those of man in being circular biconcave pale yellow disks; those of camels and dromedaries, however, are oval. The blood-corpuscles of dogs are so like those of man in size that they cannot be readily distinguished; but in most cases the size is sufficiently different to enable a safe opinion to be formed. This fact has often been used to further the ends of justice in determining whether spots of blood on the clothes of a suspected murderer were really due to the cause assigned by him. The red blood-corpuscles of birds, reptiles, amphibians, and fishes cannot be confounded with those of man, since they are oval and contain a nucleus in the centre such as is not found in our red corpuscles.
Which kind is most numerous? Give some idea of their num. ber. Why does the blood look uniformly red to the unaided eye?
Describe the form of human red blood-corpuscles. What is the color of one seen by itself with a microscope? How may we show that blood looks red only when its corpuscles are crowded close together? How do the red corpuscles become arranged soon after blood is drawn ?
Describe the corpuscles of most mammalia. How do those of camels and dromedaries differ from the corpuscles of other mammals? Why cannot a dogs blood be easily distinguished from human blood?