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V. — Comparative Photographs of Blood-disks. 
By a. Gulliver, F.E.C.S., F.E.S. 
My note on this subject, in a late number of tbe ' Monthly Micro- 
scopical Journal,' appears to have produced an impression that I 
was pretending to decide the relative claims of different American 
microscopists to the first invention or preparation of the specimens 
therein noticed. Whereas nothing was farther from my intention, 
which was simply to give such a notice of this kind of American 
work as might be interesting in Europe ; for, as to the question of 
priority, I never then had a thought or any precise knowledge, 
nor can I now attempt to judge of a subject which could be better 
decided in America than here. But it is due to Dr. J. Gr. Kichard- 
son to state that his photograph, showing in one field of vision the 
blood-disks of man and the pig, was the first of the kind seen by 
me, and I suspect was originally noticed by the Editor of the 
* Monthly Microscopical Journal ' some months ago. Since then I 
have seen similar photographs, by Professor Thomas Gr. Wormley, 
of the blood-disks of the cat and human subject. And in the 
'American Naturalist,' May 1876, there appeared a short editorial 
report of Dr. Kichardson's comparative photographs " to illustrate 
in criminal cases the distinguishable appearances of different kinds 
of blood." In the same journal. Dr. C. Leo Mees is said to have 
obtained exquisite results by a modification of Dr. Eichardson's 
process ; and this statement is justified by two slides prepared by 
Dr. Mees, and now in my possession, of the blood-disks of man and 
the dog. On these slides, and still more on those prepared by 
Professor Wormley, perfectly circular corpuscles occur, just touch- 
ing each other, so as to form rows or chains, and thus to afford 
good opportunities of deducing the mean size of the corpuscles by 
one measurement of a given number of them. But, as I have long 
since shown, the corpuscles in one species of the vertebrate class, 
as seen in a single individual thereof, vary so much in size that 
their average dimensions cannot be determined with absolute pre- 
cision ; and were this fact kept in view, much needless discussion 
might be spared. And as to the medico-legal question, probably 
neither Dr. Eichardson nor any other physiologist will affirm that 
there are not several mammals the blood-disks of which cannot be 
distinguished from those of man ; while there are many others in 
which the difference is plainly demonstrable, and this notwithstand- 
ing variations in the size of the corpuscles of this or that species. 
And hence, in spite of disturbing circumstances, the diagnosis 
between the human blood and that of many animals, such as most 
ruminants and some ferae, is always quite easy, while the corpuscles 
retain their regular appearance. But how far this is the case in 
blood-spots, such as come before the criminal tribunals, has to be 
