294. 
‘Ol mm. to 05mm. The protoplasma is colourless or slightly 
yellowish, but contains red blood-globules and pigment-gra- 
nules. The number of red blood-globules is from one to eight ; 
or in pathological conditions even as many as thirty or fifty. 
Pigment-granules occur with or without the blood-dises, and 
are sometimes three or four times as large. 
These cells Bizzozero declares without hesitation to be 
concerned in the destruction of blood-discs, and compares 
them to the similar forms described by Kolliker in the 
spleen. 
The blood-vessels are described by Bizzozero (agreeing 
with Neumann) as being extremely abundant in the red 
medulla, and composing more than the half of its substance. 
He has observed capillaries also, which the German observer 
failed to find, and has both isolated them and demonstrated, 
by silver injections, their longitudinal spindle-cells. 
The arteries and veins form a kind of framework, in the 
interstices of which are contained the proper elements of the 
medulla. While Neumann finds the red blood-cells always 
within the vessels, Bizzozero observed his cells containing red 
blood-globules always outside the vessels. The medullary 
cells are scattered in a quite disorderly manner in the 
meshes of the vascular network; the “‘ gigantic”’ cells occur 
at intervals, and separated by more or less considerable 
masses of medullary cells. The connective tissue-cells, with 
their prolongations, form a sort of network, which is demon- 
strated very clearly on teazing out sections of the medulla 
hardened in potassium bichromate, or, better, in osmic 
acid. 
The gelatinous medulla differs from the red by its abundant 
intercellular substance. While in the red medulla the spaces 
between the vessels are almost filled with cellular elements, 
there is in the gelatinous a large quantity of amorphous, 
translucent, colourless, or faint yellowish substance, which 
coagulates with dilute acetic acid, and dissolves in an excess 
of that reagent. Moreover, the nucleated blood-cells, and 
especially the cells containing blood-globules or pigment, are 
rare. 
The yellow medulla is distinguished by its richness in fat- 
cells from both the others. Various transitional forms 
between these three varieties of medulla may be met with. 
These facts of structure, as well as the variations met with 
in pathological conditions, illustrate the great analogy of the 
medulla with the spleen. 
Some experiments were made to determine the effect of 
starvation on the medulla. In a healthy, well-fed rabbit the 
