(2) Camel tribe, in which the corpuscles are oval in form, but non-nucleated.
(3) In birds, fishes, reptiles, and amphibians the red corpuscles are oval in shape, and possess a nucleus.
Guided by the above facts, one is able to testify whether or not the corpuscles exhibit the characters of mammalian blood.
Many attempts have been made with a view to establishing a reliable means of differentiation between the red blood corpuscles of man and other mammals (the camel excepted), and with a certain degree of success, such as might be expected, under select conditions favourable to histological research, but which do not obtain in medico-legal practice. Differences in size of the red corpuscles, as revealed by micrometric measurement, have been suggested as a possible means of distinguishing between the blood of different mammals. Of the common animals, the red blood corpuscles of the sheep present the most marked difference in size compared with those of man. The following table of the dimensions of red blood corpuscles is derived from measurements made by Treadwell, and quoted by White (The Medico-Legal Journal, New York, 1895):
| μ. | |
| Human | 7.940 |
| Dog | 6.918 |
| Rabbit | 6.365 |
| Ass | 6.293 |
| Pig | 6.101 |
| Horse | 5.503 |
| Cat | 5.463 |
| Ox | 5.436 |
| Sheep | 4.745 |
Menstrual blood contains no fibrin, has an acid reaction due to the vaginal mucus which keeps it fluid, and contains squamous epithelial cells. None of these characters can be differentiated on fabrics, especially when contaminated with urinary stains in addition. Hence, in cases of alleged rape, no distinction can be drawn between blood-stains on the underclothing of the female, which may have arisen from hæmorrhage the result of violence to the sexual parts, and those which might have arisen from the ordinary menstrual flow or metrorrhagia. The detection of spermatozoa, however, would add considerable value to the observation.
Fig. 8.—Measurement of Blood Corpuscles.
Photo-micrograph of human red blood corpuscles, × 800. Each corpuscle in diameter covers two divisions of the scale. Compare with sheep‘s blood, [Fig. 9].
(R. J. M. Buchanan.)