76 THE BODY AT WORK 



ferments are secreted as zymogens, which require to be in- 

 fluenced by a kinase before they acquire fermentative activity. 

 So, too, must thrombogen be changed into thrombin, under 

 the influence of thrombokinase, before it can act upon 

 fibrinogen. Almost all tissues yield the kinase which actuates 

 fibrin-ferment. The utility of this provision is manifest. A 

 bird's blood contains everything necessary to form a clot with 

 the exception of thrombokinase. The injury which brings the 

 blood into contact with a broken surface supplies this ferment 

 of the ferment. Fibrin-ferment, rendered active, at once 

 changes fibrinogen into fibrin. The same interaction is neces- 

 sary before the blood of a mammal is susceptible of clotting. 

 But a mammal's blood is even readier to clot than is the blood 

 of a bird ; for not only will a broken surface provide it with 

 thrombokinase, but the leucocytes contained within the blood, 

 when injured, also yield it. And the leucocytes are exceed- 

 ingly sensitive of any change of circumstance ; on the slightest 

 indication that conditions are not normal they set free, perhaps 

 owing to their own disintegration, the kinase which turns 

 thrombogen into thrombin. 



There is a constitutional condition, fortunately rare, in 

 which blood does not coagulate. A person subject to this 

 abnormality is said to suffer from haemophilia. It is alleged 

 that this condition is due to deficiency of lime in the blood ; 

 and the deficiency of lime is said to be due to excess of phos- 

 phates. The subject suffers from phosphaturia. His kidneys 

 get rid of the superabundance of phosphates by excreting 

 them in combination with lime. If this explanation be correct, 

 there is a chronic insufficiency of lime in the blood, because it 

 is being constantly withdrawn in the process of removing 

 phosphates. 



The difficulty in the way of establishing a complete theory 

 of the coagulation of blood increases when the phenomena of 

 incoagulability are considered. Blood may be rendered in- 

 capable of clotting in a variety of ways. Leeches and other 

 animals which suck blood have the capacity of rendering it 

 incoagulable. If the heads are removed from a score of 

 leeches, thrown into absolute alcohol, dried, ground in a 

 pepper mill, extracted with normal saline solution, a dark 

 turbid liquor is obtained. This liquor, after filtration and 



