BLooD AND LYMPH. 39 
trated an opaque white appearance similar to that seen in the 
peripheral nerves, and is hence described as white substance. 
In the spinal cord (Fig. 19) the grey substance is disposed as a 
central core, the white substance as a peripheral investment. 
A similar relation is found in the basal portion of the brain, but the 
characteristic pattern in the cerebral hemispheres and in the cere- 
bellum is one in which the grey substance forms a peripheral, 
investing, or cortical layer. 
5. Blood and Lymph. 
Blood (Fig. 20) is fundamentally a cellular material, but owing 
to the fact that the cells or corpuscles are contained in a fluid 
medium, the plasma, it does not take on the features of the ordinary 
tissues of the body. It is for this reason also that, notwithstanding 
its important function, the appearances pre- 
sented by the blood in dissection especially of 
preserved animals are negligible. The cellular Fa 
materials consist of (a) erythrocytes or red oe 
blood cells, microscopic circular discs of fairly 
definite though not rigid contour, containing 
in the adult condition no nucleus. They have a Borneo sthe BEI 
yellow color, which is due to the presence of —' ‘°°? Profle: 
haemoglobin, and which gives to blood its deep red color when seen 
in bulk. The haemoglobin is the specific carrier of oxygen which it 
combines chemically. Arterial, oxygenated blood is bright red, 
while venous blood is dark red or bluish. The number of red blood 
cells is relatively somewhat greater in the rabbit than in man, 
there being over six millions contained in each cubic millimetre. 
The cells are formed in the vascular area of the embryo, later in 
the spleen and liver, and finally in the marrow of bones; (b) 
leucocytes and lymphocytes, also termed white or colorless 
blood cells. They are amoeboid, nucleated cells, present in much 
O = 
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— 
=3 
smaller numbers in blood, and in lymphatic vessels, and are formed 
in the lymph glands and spleen. They are capable of passing 
through the walls of the smaller vessels, and occur more or less 
throughout the tissues, where they have the function of carrying 
materials or of ridding the bedy of injuricus substances and bac- 
