60 SCIENCE “PROGRESS 
of this globulin which was known as fibrin. In the theory of 
Lilienfeld,! though the existence of thrombin-is accepted, the 
idea that it plays any important part in the process of coagula- 
tion is denied, and the behaviour of calcium in the process is 
regarded as identical with the views suggested by Arthus, 
for whom fibrin was a calcium compound of fibrinogen or a 
thrombosin curd. Alexander Schmidt, however, denied the 
specific action of calcium for either phase of the coagulation 
process; its presence in a coagulable fluid only favours the 
conversion of a zymogen into an enzyme and the formation of 
fibrin from fibrinogen. He therefore included calcium salts 
with these substances, which, like strontium, and possibly 
barium, exert a directly favouring influence on the rate and 
extent of the coagulation process. 
These conflicting views have been completely explained by 
Hammarsten,” whose researches were directed towards affording 
a sufficient answer to two questions : 
1. Are salts of lime absolutely necessary in order that fibrin- 
ferment shall act upon fibrinogen ? 
2. Can the whole coagulation process in its two phases occur 
in the absence of calcium salts ? 
Hammarsten showed that the total calcium content of blood 
is in two states. That portion which is in solution can alone 
be precipitated by oxalate, while another portion, which is 
probably united in organic combination with the proteins of 
the plasma, cannot be detached. The non-coagulability of 
oxalated plasma is therefore a matter related to that fraction 
of the calcium which can be precipitated. When oxalate-plasma 
is cooled to 0°, Pekelharing had already shown that a granular 
precipitate gradually separates out; and in proportion as this 
occurs, so does oxalate-plasma lose its peculiar property of 
coagulating on the addition of calcium chloride. It was a 
logical deduction that this separated material was essential for 
coagulation, and from the supernatant oxalated plasma Hammar- 
sten precipitated a calcium-free fibrinogen by lime-free sodium 
chloride, and found that a calcium-free fibrinogen could be caused 
to clot on the addition of a calcium-free solution of thrombin. 
By this experiment it was conclusively proved that the presence 
of calcium is quite unnecessary for the conversion of fibrinogen 
' See Text-book of Physiology, ed. by Schafer, vol. i. p. 172.’ 
* Lettschrift f. physiol, Chemie, xxii. p. 333, 1896, and 72d. xxviii. 1899 
