56 SCIENCE PROGRESS 



horse, together with the contained blood, by ligaturing the 

 vessel in two places. The operation was carried out aseptically, 

 with a minimum amount of damage. The corpuscles settled 

 down, and from the uncoagulated plasma an insoluble fibrinogen 

 separated out at 56 C. A substance varying in activity, which 

 is destroyed by heat, can be obtained from coagulating or 

 coagulated blood. This is thrombin, or fibrin-ferment (Alexander 

 Schmidt, 1872), which does not exist in circulating blood, and 

 therefore coagulation does not occur during life ; but thrombin 

 appears when blood dies, and the surplus which is not used is 

 found subsequently in the serum. The ferment is destroyed by 

 boiling. It cannot be obtained as a pure product. We recognise 

 the substance, as is the case with all ferments, by its specific 

 action, that of converting a soluble fibrinogen into an insoluble 

 fibrin. Under the microscope certain changes can be witnessed 

 in a film of shed blood. From isolated highly refracting bodies, 

 the blood-platelets, or from groups of these, strands of less 

 refractive material can be seen to extend, form a network, 

 entangle both the red and white corpuscles, and form a clot 

 (Mrs. E. Hart, 1879 l ). 



These statements embody the main facts known in 1880, and, 

 though they may be found in all text-books of physiology, it 

 is convenient to mention them here, since the workers of the 

 past twenty-five years have been compelled to take these certain 

 facts into account, and, indeed, no theory of coagulation can 

 ignore them. Theories are not necessarily explanations, and 

 the successive output of work in connection with coagulation 

 has tended to the creation of a somewhat mystifying terminology 

 and to the construction of innumerable theories. Apart from 

 original papers, special contributions in English, 2 French, 3 

 and German volumes, 4 together with the admirable article by 

 Morawitz, 5 have rendered it possible to sift out the less definite 

 from those more definite facts which have thrown light on the 

 nature of the coagulation process both within and outside 

 the body. 



The work of Alexander Schmidt himself, apart from that 



1 Quart. Journ. of Microscopic Science, xxii. 1882. 



2 E. A. Schafer, Text-book of Physiology, vol. i. p. 168, 1898. 



3 Arthus, La Coag, du Sang : Paris, 1899. 



4 E. Schwalbe, Untersuch. iiber Blutgerin?tung, 1890. 



5 Ergebnisse der Physiol, p. 307, 1905. 



