1078 



GENERAL ANATOMY OR HISTOLOGY. 



FIG. 598. Human red blood-corpuscles. Highly magnified, 

 a. Seen from the surface. 6. Seen in profile and forming 

 rouleaux, c. Rendered spherical by water, d. Rendered 

 crenate by salt solution. 



erythrocytes, (2) colorless corpuscles or leucocytes. A third variety, the blood- 

 platelets, are of subsidiary importance. 



1. Colored or red corpuscles (erythrocytes}, when examined under the micro- 

 scope, are seen to be circular disks, biconcave in profile. They have no nuclei, 



but in consequence of their bicon- 

 cave shape present, according to 

 the alteration of focus under an 

 ordinary high power, a central 

 part, sometimes bright, sometimes 

 dark, which has the appearance 

 of a nucleus (Fig. 598, a). It is 

 to their aggregation that the blood 

 owes its red hue, although when 

 examined by transmitted light 

 their color appears to be only a 

 faint reddish yellow. Their size 

 varies slightly even in the same 

 drop of blood ; but it may be 

 stated that their ordinary diameter 

 is about -3^0 of an inch, while 

 their thickness is about ^2^77 of 

 an inch or nearly one-quarter of 

 their diameter. Besides these there are found, especially in disease (e. g., anaemic 

 conditions), certain smaller corpuscles of about one-half or one-third of the size just 

 indicated ; these are termed microcytes, and are very scarce in human blood. 

 The number of red corpuscles in the blood is enormous ; between 4,000,000 and 

 5,000,000 are contained in a cubic millimetre. Power states that the red cor- 

 puscles of an adult would present an aggregate surface of about 3000 square 

 yards. Each corpuscle consists of a colorless elastic spongework or stroma, con- 

 densed at the periphery to form an investing membrane, and uniformly diffused 

 throughout this are the colored fluid contents. The stroma is composed mainly 

 of nucleo-proteid and of the fatty substances, lecithin and cholesterin, while the 

 colored material consists chiefly of the respiratory proteid, hcenwglobin, which 

 contains a proportion of iron in addition to the ordinary proteid elements. This 

 proteid has a great affinity for oxygen, and when removed from the body crys- 

 tallizes readily under certain circumstances. It is very soluble in water, the 

 addition of which to a drop of blood speedily dissolves out the haemoglobin from 

 the corpuscles. 



If the web of a frog's foot is spread out and examined under the microscope, 

 the blood is seen to flow in a continuous stream through the vessels, and the 

 corpuscles show no tendency to adhere to each other or to the wall of the vessel. 

 Doubtless the same is the case in the human body ; but when the blood is drawn 

 and examined on a slide without reagents, the corpuscles often collect into heaps 

 like rouleaux of coins (Fig. 598, b). It has been suggested that this phenom- 

 enon may be explained by alteration in surface tension. 



During life the red corpuscles may be seen to change their shape under press- 

 ure so as to adapt themselves to some extent to the size of the vessel. They 

 are, however, highly elastic, and speedily recover their shape when the pressure 

 is removed. They are soon influenced by the medium in which they are placed, 

 and by the specific gravity of the medium. In water they swell up, lose their 

 shape, and become globular (Fig. 598, c). Subsequently the hemoglobin becomes 

 dissolved out, and the envelope can be barely distinguished as a faint, circular 

 outline. Solutions of salt or sugar, denser than the plasma, give them a stel- 

 late or crenated appearance (Fig. 598, d) ; but the usual shape may be restored by 

 diluting the solution to the same specific gravity as the plasma. The crenated 

 outline may be produced as the first effect of the passage of an electric shock ; 

 subsequently, if sufficiently strong, the shock ruptures the envelope. A solution 



