IO 
HEMOLYMPH NODES OF THE SHEEP 
of exposure to oxygen, for example. It was also noticed that in winter 
the color of nodes in situ on the carcasses was darker than in summer, 
which difference was evidently due to the fact that the severe cold of an 
open abattoir in a northern climate retarded the process of spontaneous 
post-mortem oxygenation, by making the overlying layers more im- 
pervious to the oxygen of the air, or by affecting the rate of chemical 
interchange. Ordinarily the change in color begins immediately after 
evisceration, and is noticeable at first in the smallest and most exposed 
node. However, the rate of the change of color is also dependent upon 
the presence and the thickness of the surrounding layer of blood in the 
peripheral blood space. That not all nodes change from a venous color 
when the abdomen is opened to a bright red upon exposure to the air 
later may, of course, be due to these and to other facts, as well as to 
variations in thickness of the capsule and the overlying fat. An examina- 
tion of several hundred carcasses immediately after the abdomen was 
opened showed that the variations in color are very slight at this time. 
Very occasionally, however, a small scarlet node is seen among a group 
of venous-colored ones, which fact can probably be explained by differ- 
ences in the circulatory conditions within the node. The peculiarly mot- 
tled appearance of nodes which often does not become very evident until 
fixation and hardening, can likewise be explained satisfactorily by pe- 
culiarities of structure. In these latter nodes, for example, the peripheral 
blood space is encroached upon here and there intra vitam, and often so 
as a result of shrinkage during fixation and hardening, by the lymphatic 
tissue — usually by follicles — and may hence be completely obliterated at 
some places. Wherever this occurs a gray patch or streak bordered by 
a deeper-colored area will be found on the surface. For like reasons 
the entire absence of the peripheral blood space before or after fixation 
might give a whole node a grayish color, or if absent over but a part of 
the node it might result in an appearance which might suggest that one 
portion has the character of a hemolymph and the other that of a lymph 
node, or that there are mixed or composite nodes. Besides these factors, 
still others, to be discussed later, have an important bearing upon the 
question of external appearance. 
Exposure of hemolymph nodes to carbon dioxide, on the contrary, 
never produced the slightest visible changes in color. Such as were 
chocolate-colored when exposed to this gas remained so. The same was 
true if they were of any other shade. But if nodes thus exposed for a 
short time were still sufficiently fresh, subsequent exposure to oxygen 
would result in a change to the usual bright-red color of freshly coagu- 
