The Cell 15 



about 7.5 /«■ in diameter. Cells of voluntary muscles, although but a few /* 

 in diameter, may be several centimeters long. Human nerve cells' may be 

 as much as a meter in length, and in larger animals there are nerve cells 

 of even greater length. The largest single cells are the yolks of birds' 

 eggs; these cells do not contain more protoplasm than do microscopic 

 cells, 5 but they are swollen by the great amount of foreign material present. 



Fig. 3. Diagram showing the forms of certain of the blood corpuscles as enlarged 

 1200 diameters. A, B, largest outline of red blood corpuscles. C, D, F, cross section 

 of red corpuscles, perpendicular to largest outline. Red corpuscles as prepared on 

 microscope slides usually have the form corresponding to D, sometimes that corres- 

 ponding to C or F. Histologists differ as to which is the normal form of the cor- 

 puscles in the blood vessels of the living animal. G, H, K, white corpuscles; G, lym- 

 phocyte ; H, large mononuclear leucocyte at rest ; K, the same in motion. 



The protoplasm within the cell, exclusive of the nucleus, is called 

 cytoplasm. Under examination, the cytoplasm is sometimes homogeneous 

 in appearance, sometimes it appears to be finely granulated, and sometimes 

 it appears to consist of a reticulated or meshed structure of fine threads, 

 the spongioplasm, the meshes of which are filled with a semi-fluid, the 

 cytolymph or hyaloplasm. Some histologists hold that the typical 

 structure of the cytoplasm is alveolar, that is, made up of globular droplets 



. s Tb,e, protoplasm and nucleus contained in the yolk of a hen's egg is about 1% of 

 the ' germinal disc ' which is visible on one side of the yolk. A human egg is 

 about 170^ in diameter. 



