DISEASE-RESISTING FUNCTIONS OF THE BLOOD 319 



either with the effect of hastening the result or of retarding it 

 or even preventing it altogether. Anything which quickens the 

 disintegration of the blood-plates, as the application of a hand- 

 kerchief to a wound, which acts by increasing the foreign surface 

 in contact with the blood, makes the blood clot more quickly. 

 The application of heat has this same effect; probably it acts both 

 by increasing the rate of destruction of blood-plates and by has- 

 tening the chemical reactions involved in the process as a whole. 

 Cold, as would be expected, has the converse effect. An increase 

 in the calcium content of the blood shortens the coagulation time. 

 Coagulation may be retarded, as we have seen, by cold or by de- 

 priving the blood of its calcium content. Blood drawn into a 

 strong solution of sodium or magnesium sulphate and well mixed 

 will not clot, these salts appearing to interfere in some way with 

 the formation of the thrombin; such " sal ted" blood will clot if 

 thrombin is added or if diluted sufficiently with water. 



An interesting fact, recently established, is that an increase in 

 the amount of adrenin (p. 199) in the blood hastens its coagulation. 

 This result cannot be secured by adding the hormone to the blood 

 as it is drawn, but only by introducing it into the circulation; show- 

 ing that the quickening of the clotting process is not a direct result 

 of the chemical action of adrenin on the blood, but is brought about 

 indirectly through the influence of the adrenin on some of the 

 tissues through which the blood circulates. This property of 

 adrenin is looked upon as a phase of its general function as an 

 emergency hormone, for in time of stress and possible bodily injury 

 prompt coagulation of the blood would tend to stop a hemorrhage 

 quickly and so conserve the precious liquid. 



" Bleeders." There is a pathological condition, fortunately not 

 very common, known as hemophilia, in which the blood will not 

 clot. Persons suffering from this disease are called bleeders. Such 

 persons are in danger of bleeding to death from slight wounds; a 

 nosebleed, or the bleeding which follows the extraction of a tooth, 

 becomes in such persons an affair of the utmost gravity. Various 

 explanations have been offered to account for this disease; at 

 present it is believed to be due to a deficiency of prothrombin. 



This condition is usually hereditary. An interesting fact in 

 connection with it is that whereas the disease itself appears only 

 in males, its transmission seems to be confined wholly to females; 



