THE BLOOD. 169 



five forms are believed to correspond to as many stages of develop- 

 ment. The third form (the colorless nucleated cell) is, however, the 

 highest stage of development in the white blood of the invertebrate 

 animals. The "colored nucleated cell" (fourth stage) is the highest 

 form in the oviparous mammalia; while the "colored non -nucleated 

 cell" is the perfect blood-cell of the mammalia. It does not, how- 

 ever, follow that the human blood-cell passes through the five stages 

 mentioned by Mr. Jones, nor that any stage corresponds precisely 

 with one of these. There is, however, a general correspondence 

 not without interest. The following account of their development 

 is extracted from Mr. Paget's lectures, 1 and which may be accepted 

 as the most reliable hitherto. Fig. 102 represents the five stages of 



Development of the red from the colorless corpuscles of the blood. A. Cytoid corpuscle. B. Same, 

 being converted into a red corpuscle, c. Cytoid corpuscle with its membrane raised by the action 

 of water. D. Same, having lost most of its granules. E. Same, acquiring color ; a single granule 

 remaining like a nucleus. F. Perfect red corpuscle. 



development of the colorless into the colored cell ; though the im- 

 probability has already been remarked that all the cytoid corpuscles 

 are thus transformed (p. 161): 



"The white corpuscle, at first tuberculated, containing many gran- 

 ules, and darkly shaded (A), becomes smoother, paler, less granular, 

 and more dimly shaded or nebulous (B). In these stages the 

 cell- wall may be easily raised from its contents by the contact and 

 penetration of acetic acid, or by the longer action of water (c) ; and, 

 according to the stage of development, so are the various appear- 

 ances which the contents of the cell thus acted on present. In the 

 regular progress of development, it becomes at length impossible 

 to raise the cell- wall from its contents (D). Then the corpuscles 



1 On the Life of the Blood. 1848. 



