Blood-cor]puscles of A. tridactylum^ &c. By Br. Schmidt. 109 
animals of the remaining classes of the Vertebrata. While the 
latter, to which those of the Amphiuma and the Frog, discussed in 
the preceding pages, belong, are distinguished by their large size, 
by their oval and bi-con vex form, and moreover by enclosing a 
conspicuous nucleus, giving them the character of a complete 
organic cell, the blood-corpuscles of the Mammalia are more minute 
in their dimensions, round and hi-concave in form, and embracing 
no nucleus, they rather represent an organic cell of a more simple 
construction. Accessible at all times, the blood-corpuscles of Man, 
especially, have always been a favourite object for microscopic 
examination ; and owing to the important part which they play 
in the organism of Man, their nature has been studied and dis- 
cussed by anatomists and physiologists over and over again. For 
this reason I should forbear from making any further remarks on 
the structure and nature of these bodies, if I were not conscious of 
the fact that, notwithstanding the numerous investigations already 
made, the subject has not in all cases been fairly dealt with, and 
is therefore not yet exhausted. On the contrary, in order to 
finally settle the question whether the coloured blood-corpuscle of 
Man possesses or not an enveloping membrane, a re-examination 
of the subject becomes necessary, particularly by those histologists 
who deny the existence of such a membrane in any form. The 
coloured blood-corpuscle of Man shows a double contour under 
various circumstances and conditions, indicating the existence, if 
not of an enveloping membrane, at least of a membraneous layer 
on its surface ; and anyone who chooses to examine these bodies in 
the manner to be described hereafter, will be convinced of this 
fact. 
It is an admitted fact that the coloured blood-corpuscles of 
Man represent minute bi-concave disks (Fig. 59, a and h) with 
rounded margins, and of a diameter of about mm. They are 
very delicate in substance, and being elastic and flexible in an 
unusually high degree, are enabled to resume always their original 
form, when distorted by mechanical causes. In fact, the momentary 
changes of form, which they are constantly undergoing when float- 
ing in the liquor sanguinis, are owing to the great delicacy and 
elasticity of their protoplasm. In examining them under the 
microscope with a sufficient amplification, we observe that the most 
feeble current arising in the liquid in which they float, disturbs 
their form, either directly or by causing individual corpuscles to 
touch each other in passing, or also by calling forth a mutual 
pressure in a greater number of blood - corpuscles. When a 
coloured blood-corpuscle of Man is examined in the state of rest 
from the front, its outline appears perfectly round. Being put in 
the proper focus, so that its outlines appear the most distinct, its 
centre, to the extent of about one-third of the whole diameter. 
