7 6 Similarity between the Red Blood-corpuscles of Man, <f -c. 
of thin films dried on glass ; and if it is impossible in the latter 
case to ascertain by the microscope that the sample submitted is 
human blood, it would be absurd to hope to do better in the former. 
I cannot, however, refrain from expressing my conviction that Carl 
Schmidt was quite as accurate in measuring his samples as Dr. 
Richardson in measuring his, and that the latter has underrated the 
variations in size which the dried corpuscles may present under 
various conditions. 
I may also call attention, in this connection, to the effect of 
water on the diameter of the corpuscles. Mr. Gulliver has pointed 
out that if “ water be mixed with blood, the disks immediately 
become much enlarged and spherical, quickly losing their colouring 
matter ; and yet if the whole of this be thus removed, after a while 
the outlines of the disks, very faint indeed, may frequently be recog- 
nized, diminished considerably in diameter and apparently quite 
flat.” * 
In another place he relates that “ some human corpuscles 
having an average diameter of ^Vg-th of an inch measured only 
TsVtfth of an inch after the whole of their colouring matter had 
been separated in this manner.” f Suppose, now, the case of blood 
mixed with water and afterwards dried, as, for example, in the case 
of an unsuccessful attempt to wash away the blood while fresh ? 
In conclusion, then, if the microscopist, summoned as a scientific 
expert to examine a suspected blood stain, should succeed in making 
out the corpuscles in such a way as to enable him to recognize 
them to be circular disks, and to measure them, and should then 
find their diameter comes within the limits possible for human 
blood, his duty, in the present state of our knowledge, is clear. He 
must, of course, in his evidence present the facts as actually 
observed, but it is not justifiable for him to stop here. He has no 
right to conclude his testimony without making it clearly under- 
stood, by both judge and jury, that blood from the dog and several 
other animals would give stains possessing the same properties, and 
that neither by the microscope, nor by any other means yet known 
to science, can the expert determine that a given stain is composed 
of human blood, and could not have been derived from any other 
source. This course is imperatively demanded of him by common 
honesty, without which scientific experts may become more 
dangerous to society than the very criminals they are called upon 
to convict. 
* ‘ London and Edinburgh Philosophical Magazine,’ vol. xvi. (1840), p. 10G. 
t Ibid., vol. xxi. (1842), p. 108. 
