THE CELLULAR CHANGES OF AGE 77 



may interest you to know that it was not until 1902 

 that the actual shape was correctly recognised. The 

 corpuscles are so small that about 5,000,000 occur in 

 a cubic millimetre of blood. The picture now before 

 us illustrates the life history of these cells. 1 In the 

 earliest stage of their cytomorphosis the cells have 

 each a well formed nucleus, Fig. 25, No. i, with a min- 

 imal amount of protoplasm around it, indeed the pro- 

 toplasmic envelope is so exceedingly thin that earlier 

 observers thought the corpuscles began as naked 

 nuclei without a cell body. 2 In the next stage, No. 

 2, the cell body has grown so that there is more pro- 

 toplasm than before in proportion to the volume of 

 the nucleus. The cell body around the nucleus is at this 

 time loading itself with haemoglobin, the red substance 

 which plays, as you all know, so important a part in 

 respiration. The enlargement of the cell soon reaches 



Weidenreich {Archiv f. mikrosk. Anat., LXI., p. 61), whose observations have 

 been confirmed in my laboratory, especially by Professor F. T. Lewis (Journ. 

 Med. Research^ x., 513, 1904). 



1 As regards the drawings in Figure 25, it should be stated that from each 

 embryo a single corpuscle was selected by me as typical. In the specimens cor- 

 puscles in many different stages of development are found together and the se- 

 lection of a typical corpuscle is difficult. The choice is necessarily somewhat 

 arbitrary. The drawings illustrate the progress of development correctly, except 

 that the transition from the last nucleated stage, No. 6, to the final cup-shaped 

 stage, No. 8, is still subject to discussion, but No. 7 was drawn from an actual 

 corpuscle, which had certainly lost its nucleus and become smaller, and apparently 

 was just beginning to assume the cup-shape. How the nucleus disappears is not 

 known with certainty; there are two principal views, the first that the nucleus 

 is extruded, the second that it is dissolved by the rest of the cell. The problem 

 of the disappearance of the nucleus, though very important cytologically, is of 

 secondary interest for the main purpose of the present lecture. 



2 For example, F. M. Balfour, Works, vol. i., p. 50. 



