THE BLOOD 225 



the microscope it is possible to detect here and there 

 among the host of red corpuscles bodies of a different 

 type. These are the white or, better, colorless cor- 

 puscles. There may be one of these to a thousand reds. 

 Several kinds are recognized and the proportion existing 

 between them is of interest to the practitioner. Of all 

 it may be said that they are free from hemoglobin and 

 that they are complete, nucleated cells. We speak 

 confidently of them as living. Some originate along 

 with the red corpuscles in the bones, others in kernels of 

 tissue known as lymph nodes, of which more will be 

 said. 



The majority of the white cells are of the ameboid type 

 to which reference was made in Chapter IV. There we 

 indicated the power which these cells have to make their 

 escape from the capillaries and their capacity for devouring 

 bacteria. Other services than this have been conjectured 

 but without very tangible evidence. Thus it has been 

 thought possible that the white cells of the blood have 

 to do with the assimilation and working over of the foods 

 to adapt them to the requirements of the tissues. 



Blood-plates. When blood has been prepared by 

 special methods for microscopic study there may be 

 found in it quite numerous bodies of a smaller size than 

 either the red or the white corpuscles. These are the 

 blood-plates. They were formerly held to be mere 

 particles of debris but the belief is now general that they 

 are perfect though unusually minute cells. They are 

 remarkably perishable and stand in a certain relationship 

 to a curious property of blood, its coagulability. This 

 must be briefly discussed. 



Coagulation. Blood in the vessels is quite free-flow- 

 ing; it is probably less viscous than is commonly sup- 

 posed, for we are apt to see it when it is approaching 

 coagulation. The capacity which it exhibits to set into a 

 jelly when shed has a manifest value. It lessens and 

 often completely checks hemorrhage by sealing over the 

 cut surface. There are individuals whose blood does 

 not coagulate and they are in grave danger of bleeding 



15 



