6 



THE BLOOD. 



a century later, William Hewson described another kind of corpuscles in the 

 blood, much less abundant than the red, which are now known under the 

 name of white globules, or leucocytes. 



Without following the progress of microscopical investigations into the 

 constitution of the blood, it may be stated that it is now known to be com- 

 posed of a clear fluid, the plasma, or liquor sanguinis, holding certain corpus- 

 cles in suspension. These corpuscles are of three kinds : 



1. Red corpuscles ; by far the most abundant, constituting a little less 

 than one-half of the mass of blood. 



2. Leucocytes, or white corpuscles ; much less abundant, existing only in 

 the proportion of 1 to 750 or 1,000 red corpuscles. 



3. Blood-plaques ; varying in size, shape and number. 



Red Corpuscles. These little bodies give to the blood its red color and 

 its opacity. They are organized structures, containing organic nitrogenized 

 and inorganic matters molecularly united and a little fatty matter in union 

 with the organic constituents. They constitute a little less than one-half the 



mass of blood, and according to the 

 observations of all who have investi- 

 gated this subject, are more abun- 

 dant in the male than in the female. 

 The form of the blood-corpuscles 

 is peculiar. They are flattened, bi- 

 concave, circular disks, with a thick- 

 ness of one-fourth to one-third of 

 their diameter. Their edges are 

 rounded, and the thin, central por- 

 tion occupies about one-half of their 

 diameter. Their consistence is not 

 much greater than that of the plas- 

 ma. They are very elastic, and if 

 deformed by pressure, immediately 

 resume their original shape when 

 the pressure is removed. Their spe- 

 cific gravity is between 1088 and 

 3105, considerably greater than the specific gravity of the plasma, which is 

 about 1028. 



When the blood has been drawn from the vessels and coagulates slowly, 

 Ihe greater density of the red corpuscles causes them to gravitate to the lower 

 portions of the clot, leaving the white corpuscles and fibrin at the surface. If 

 coagulation be prevented by the addition of a small quantity of sodium sul- 

 phate, there is quite a marked gravitation of red corpuscles after standing 

 for some hours. 



The peculiar form of the blood-corpuscles gives them a very characteris- 

 tic appearance under the microscope. Examined with a magnifying power 

 of between three hundred and five hundred diameters, those which present 

 their flat surfaces have a shaded centre when the edges are exactly in focus. 



FIG. 1. Human blood-corpuscles; magnified 1,450 



diameters (Sternberg). 



This figure also shows a leucocyte containing four 

 fatty granules. 



