286 THE HUMAN BODY 



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

 what is lacking in the blood of " bleeders " is not known, it may 

 be any one or a combination of several of the elements whose 

 united action is essential to the process of clotting. 



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; 

 a father who was a "bleeder" would have no children suffering 

 from the condition nor would his sons, but if his daughters had 

 sons they would probably be bleeders. 



Blood Transfusion. The restoration of blood lost in severe 

 hemorrhage, or the replacement of diseased blood by healthy 

 blood through transfusion from the veins of one individual to 

 those of another has long been a dream of physicians and physi- 

 ologists. The early attempts to treat disease by this method were 

 more often fatal than not because the blood to be introduced into 

 the circulation had to be defibrinated. This process, as we have 

 seen, preserves the blood in a liquid condition, but it leaves in it 

 large quantities of the exciting agent to coagulation, thrombin. 

 When such blood was introduced into the circulation it usually 

 induced prompt clotting of the blood already there, with im- 

 mediately fatal results. The fuller knowledge of the mechanism 

 of blood-clotting gained of late years has made it clear that blood 

 transfusion need not be followed by clotting if the transfer of 

 blood be made without exposing it at any time to a foreign sur- 

 face, such as favors the disintegration of the blood-plates. In 

 accordance with this idea an ingenious method has recently been 

 developed whereby an artery of one individual can be brought 

 into communication with a vein of another and the blood allowed 

 to flow naturally across the living channel thus formed. Many 

 lives have been saved by this method during the few years since 

 its first application, and it promises to fulfil in some degree, at 

 least, the early hopes of the medical world. It should be noted 

 that successful blood transfusion requires that the blood to be 

 introduced be taken from an individual of the same species as the 

 one who is to receive it; hence human beings who require blood 

 must receive it from other human beings, and not from animals. 

 One of the most curious facts brought out in connection with the 

 study of the disease-resisting mechanism of the Body is that to 



