i So THE BLOOD. 
as supposed by Lowit 1 and by Wright, 2 but by causing their accumula- 
tion within the tissues (? capillary blood vessels). For a very short 
time after their almost complete disappearance from the blood they 
begin gradually to reappear, and in one experiment C.J. Martin found 
that the full number had reappeared within as short a time as fifteen 
minutes. 3 Moreover, if such disintegration really took place one would 
expect the coagulability of the blood to be visibly increased, from the 
setting free of their nucleo-proteids, whereas it is actually diminished 
or abolished. Nevertheless, those substances, such as snake venom, 
nucleo-proteids, and colloids, which in larger doses produce intravas- 
cular coagulation, may in part act by causing disintegration, if not of 
leucocytes at least of red corpuscles which also contain nucleo-proteids. 
That this occurs to some extent is shown by the fact that the serum is 
usually tinged by haemoglobin. And even without actual disintegration 
the permeability of the corpuscles may become altered, and nucleo- 
proteid shed out. 
But there is another tissue upon which the reagent in question may 
act, namely, the epithelial cells of the blood vessels. These are in all 
probability composed of living protoplasm, and the reagents may either 
cause them to shed mil nucleo-proteid and so produce fibrin ferment, 
or, by deleteriously affecting them, may cause them to react upon the 
leucocytes which are passing along in contact with their inner surface. 
ami effect a discharge of nucleo-proteid from these cells. That snake 
venom affects the blood vessels deleteriously is shown by the capillary 
haemorrhages which are so frequently seen after poisoning by it, and 
by the rapid effect it produces on the blood circulating in the mesentery, 
if a little lie applied to the surface of that membrane. 4 The same does 
not, however, obtain with artificial colloids, nor with nucleo-proteids; 
although, witli partial blocking of the portal vein, after injection of a 
small dose, capillary haemorrhages have been found to occur in the liver. 5 
The evidence which we have had before us points to the following 
conclusions regarding coagulation : — 
1. That the coagulation of blood, i.e. the transformation of fibrinogen 
into fibrin, requires for its consummation the interaction of a nucleo- 
proteid (prothrombin) and soluble lime salts, and the consequent produc- 
tion of a ferment (thrombin). 
2. That either nucleo-proteid is not present in appreciable amount 
in the plasma of circulating blood, or that the interaction in question is 
prevented from occurring within the blood vessels by sonic means at 
present not understood. 
.">. That the nucleo-proteid (prothrombin) appears ami the interaction 
occurs, as soon as the blood is drawn and is allowed to come into contact 
with a foreign surface, the source of the nucleo-proteid being in all 
probability mainly the leucocytes (and blood-platelets?). 
4. That, under certain circumstances and conditions, either the 
nucleo-proteid does not appear in the plasma of drawn blood, or it 
appears, but the interaction between it and the lime salts is prevented 
or delayed. 
1 "Stud. z. Physiol, u. Path. .1. Blutes," Jena, 1892. 
2 Proc. Hoy. Soc. London, 1893. vol. lii. 
3 Loc. cit. 
4 Weir Mitchell and Reichert, ' : Researches upon the Venoms of Poisonous Serpents,"' 
Smithson. Contrib. Knowl., Washington, vol. xxvi. 
5 Wooldridge, Trans. Path. Soc. London, 1888, p. 421. 
