Biology 681 



The Blood-cells 



The blood-cells are of two sorts. One is active and re- 

 sembles an Amoeba in its capacity for changing its shape and 

 swallowing foreign particles: these are the white corpuscles or 

 phagocytes. On the other hand, the red corpuscles (from which 

 blood derives its colour, the liquid part or plasma being colourless) 

 are mere disks charged with haemoglobin, the pigment which by 

 its affinity for oxygen and carbonic acid gas is the vehicle of 

 respiration. 



These red corpuscles are produced in the marrow of the 

 long bones, and are continually being budded off there, to be 

 destroyed in the spleen when worn out. 



When a smooth lining to a cavity is required, as in the 

 abdominal cavity round the intestine, the cells bordering it be- 

 come flattened and pieced together like the bits of a jig-saw 

 puzzle. When, on the other hand, cells are destined to manufac- 

 ture and pour out chemical substances in other words, to become 

 part of a gland they are elongated vertically, and drops of 

 secretion can be seen within them. 



The tissues where reserve food is to be stored up in the 

 form of fat are made up of cells stretched like a tight skin over 

 the fat-droplet which they contain. When hard supporting tissue 

 is to be formed, as in the skeleton, it too is produced by the activity 

 of cells. In gristle or cartilage, for instance, the rounded cells 

 form layer after layer of glassy gelatinous material round them- 

 selves; whilst in the bone the cells are branched and arranged 

 regularly, and the material they lay down round themselves is 

 hardened with lime-salts. In the same way, the connective tissue 

 which binds all the organs of the body together is made chiefly of 

 microscopic fibres, some tough and resistant, some elastic; but 

 these are all formed by the cells lying scattered between them. 



The meat we eat is mainly muscle ; a muscle, too, is made of 

 cells. In smooth muscle, as in the bladder, the cells are very long 

 with faint longitudinal lines; but in the more efficient striped 





