182 THE Microscope. 
in the following manner: The finger is pricked and a good- 
sized drop of blood is squeezed out. This is taken immediately 
upon a cover-slip, and then as quickly as possible most of it 
is washed off by a jet of a 75 per cent. NaCl solution from a 
wash-bottle. The cover-slip is now placed on a slide, and 
transferred to the microscopic stage as quickly as possible. The 
plaques have the property of sticking to the slip, while the 
other elements are easily washed away by the jet, so that upon 
examination the whole field will be seen to be filled with 
plaques, some of them isolated, but most of them grouped in 
masses consisting of from two or three to a dozen or more. 
They are not pale and homogeneous, with a symetrical outline, 
but appear glistening and granular, and their contour, instead 
of being regularly oval or circular, has become jagged. These 
changes are the more marked the longer the time which has 
elapsed before the preparation is observed; and they may be 
seen to take place step by step while the observer watches the 
preparation. The plaques continue to undergo changes in form, 
until finally when they are grouped together only a granular 
mass is found, and the individual plaques can no longer be dis- 
tinguished clearly. “ Part passu with these changes processes 
are seen which run out from the granular masses; and when 
coagulation sets in these processes are nearly always found to 
be continuous with threads of fibrin. The threads of fibrin are 
sometimes deposited as long-needle-shaped crystalloids which 
are often seen lying free in the field, and not connected with 
the granular masses; but the greater number are formed most 
thickly around these masses, from which they often radiate as 
centres.” 
Kemp has found that when the blood-plasma is very much 
diluted but little fibrin is formed. ‘Under these circumstances 
the field is comparatively clear, and it can then be seen that no 
fibrin proceeds from the leucocytes, but all comes from the 
plaques, or is deposited freely in the field.” Hayem and 
Schimmelbusch have pointed out that fibrin may be formed 
elsewhere than around the plaques, and this view has been 
confirmed by Osler; though Bizzozero has stated that fibrin is 
deposited around the plaques and nowhere else. Osler says in 
his third lecture that it may be noticed that fibrin appears quite 
