Tue MIcROscopr. 157 
stances with which they come in contact. So long as they are 
kept in the vessels they do not seem to change more rapidly 
than the corpuscles, as Osler has found them unaltered in the 
pial vessels of man some hours after death; and well-preserved 
plaques may be found enclosed in fibrin taken from the body 
some time after death. 
What is the origin of the plaque? More than half a dozen 
answers have been given to this question, and experimental 
evidence has been adduced in support of each answer. So long 
as the red and white corpuscles were the only. recognized histo- 
logical elements of the blood it was most natural for any ob- 
server to connect the plaques and masses with one of these ele- 
ments. They have been variously regarded as hzeematoblasts, or 
young red corpuscles; as derived from the red corpuscles; as 
derived from the white corpuscles; as nuclei floating free in the © 
blood; as fibrin; and finally as independent elements. It seems 
scarcely worth the while to mention the evidence upon which 
these views have been founded. Suffice it to say that the views 
are carefully examined by Kemp, and suflicient evidence 
brought against them (save those which claim that they are 
hzematoblasts or independent elements) to render them most 
improbable. That they are not due to changes produced in 
other elements after the blood is drawn is shown by pricking 
the finger through a drop of osmic acid, by which process all the 
elements of the blood are immediately set when they leave the 
vessel. Furthermore, we could scarcely ask for more conclusive 
proof than that five competent observers—Bizzozero, Lavdovsky, 
Hlava, Schimmelbusch and Osler—have seen them circulating 
in the vessels of the mesentery, and in the uninjured vessels of 
the connective tissues of young rats. Kemp’s opinion is that 
there is no doubt that the plaques exist in the blood, and we 
have not vet sufficient evidence to believe them to be other 
than an independent morphological element—a view which is 
held by Max Schultze, Osler, Bizozzero, Laker, Lavdovsky, 
Halla and Schimmelbusch. . 
Careful and painstaking enumerations as to the presence of 
the plaques in the various acute and chronic diseases have not 
been made, but Osler draws the following conclusions from 
numerous observations: (1) The plaques are increased in all 
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