286 



THE BLOOD. 



Carbon-monoxid Hemoglobin. This derivative of hemoglobin 

 presents two bands resembling those 'of oxyhemoglobin, except 

 that they are nearer the violet end of the spectrum. 



Methemoglobin and hematin have each a characteristic spec- 

 trum. 



Development of Red Corpuscles. This is described by Schafer 

 as taking place in the following manner : In the developing 

 embryo some cells of the mesoblast become united, forming a 

 protoplasmic network. These cells are nucleated, and their nuclei 

 multiply, colored protoplasm forming an aggregation around 

 them. The protoplasm of this network is hollowed out by an 

 accumulation of fluid ; in this manner the capillary blood-vessels 

 are formed. The nuclei with their colored protoplasm are set free, 

 becoming embryonic blood-corpuscles. The blood-corpuscles are 

 at this period, therefore, nucleated cells. The corpuscles at this 

 time have a diameter of from 10 p to 16 /JL, and are spherical. 

 They possess the power of ameboid movement, and thus resemble 



70 65 



60 



55 



E b 



FIG. 156. Diagrammatic representation of the absorption-spectrum of hemo- 

 globin (reduced hemoglobin). The numerals give the wave-lengths in hundred- 

 thousandths of a millimeter; the letters show the positions of the more prominent 

 Fraunhofer lines of the solar spectrum. The red end of the spectrum is to the left. 

 The single diffuse absorption-band lies between D and E (after Eollett). 



the white corpuscles. It has been suggested that these should be 

 called blood-cells rather than blood-corpuscles. 



The liver begins to be formed about the third week of em- 

 bryonic life, and about the third month occupies most of the 

 abdominal cavity. This organ, together with the spleen, thymus, 

 and lymphatic glands, also produces blood-cells which are nucle- 

 ated, are at first colorless, and afterward acquire the characteristic 

 color. 



At a later period of embryonic life, about the second month, 

 non-nucleated disk-shaped corpuscles make their appearance. 

 These originate to some extent in connective-tissue cells, a portion 

 of the cell becoming colored, and separate into globular particles, 

 which subsequently become the discoid corpuscles. The connec- 

 tive-tissue cells afterward become hollowed out, and, joining with 

 other cells which have gone through the same process, blood- 

 vessels are formed. This later embryonic formation of blood- 

 corpuscles does not involve the cell-nuclei, as does that of the 

 earlier period. The nucleated cells are replaced by the non- 



