134 PHYSIOLOGY CHAP, 



the fibrinous clot is seen under the microscope to be infiltrated 

 with more or less altered leucocytes. 



If a silk thread is introduced into the interior of a large vein, 

 and carefully drawn out after some time and investigated under 

 the microscope, a fine coagulum will be seen to have formed round 

 the thread, which is denser in the places where the leucocytes 

 enclosed among the filaments are most numerous (Mantegazza). 



When the coagulation of a small drop of blood plasma is 

 watched under the microscope, the fibrin threads of which it is 

 constituted are often seen to spread out like rays from a centre, 

 which is formed by a leucocyte or a collection of disintegrated 

 platelets (Kanvier, Hayem, Bizzozero). 



On separating the plasma of horse's blood by cooling, and 

 filtering it through a triple layer of filter-paper, it can be obtained 

 entirely free of formed elements. In this case it will be seen that 

 the plasma left at the temperature of the environment may remain 

 fluid even after twenty-four hours. But if even a nominal amount 

 of a watery extract of leucocytes, or a little blood serum containing 

 leucocytes, be added, clotting at once occurs (A. Schmidt). 



Certain morbid pathological transudations behave exactly like 

 the cell-free plasma, e.g. hydrocele, or pericardial fluid, which are 

 free from formed constituents, and are of a similar composition to 

 plasma. Left to themselves, they remain fluid for an unlimited 

 time, but coagulate so soon as a little blood clot or serum is added 

 (Buchanan, 1835). 



When entirely freed from corpuscles by prolonged and 

 energetic centrifuging, the plasma separated from peptonised 

 blood not only does not coagulate spontaneously, but will not do 

 so on the addition of water, or when a stream of carbonic acid is 

 passed through, as is the case with peptonised plasma not wholly 

 deprived of leucocytes. But if a little clump of leucocytes and 

 platelets obtained by centrifuging be added, coagulation at once 

 occurs (Fano). 



The theory of Hayem and Bizzozero to the effect that coagula- 

 tion depends essentially on injury or destruction of the blood- 

 platelets, does not contradict the preceding theory, by which it is 

 associated with the injury or destruction of leucocytes. Assuming 

 (as seems probable from the researches of Lilienfeld, referred to in the 

 last chapter) that blood-platelets are derived from leucocytes and 

 represent the mass of their nuclei, the two points of view are quite 

 in harmony, and may be combined and enlarged into a single theory. 

 A. Petrone has recently discovered that the blood coagulates 

 firmly and rapidly in the early stages of pyrogallic acid poisoning 

 (1 per cent solution introduced per rectum for dogs and rabbits), 

 while the platelets are not injured, and even appear to increase, 

 the erythrocytes only suffering marked deterioration. The 

 analytical investigation of this complex intoxication has, however, 



