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THE BIOLOGY OF HYDRA : 1961 



beings. One such analogy is illustrated in Figure 2 which shows a 

 section of thick human skin. You will notice that there is a generative 

 zone, in which cell division and growth take place, and next to it the 

 so-called prickle cells in the spinosa in the process of differentiating. 

 Further toward the surface we see the granular layer. In addition 

 to showing a strong basophilia, due to the presence of acidic sub- 

 stances which have been identified as RNA by Leuchtenberg (22), 

 we observe in cells just distal to the granulated cells the complete 

 disappearance of these acidic substances. I believe it is likely that 

 this lysis is due to the action of lysosomes, bodies which DeDuve 

 (12) identified some years ago as contaminants in mitochondrial 

 fractions. Such structures occur in many cell types and, in the event 

 that the cells are damaged, they are activated to break down cellular 

 contents and thus clear the way for repair processes. In this present 

 case, they appear to hydrolyze all of the cell contents except, pre- 

 sumably, keratin and a few other substances. 



Fig. 3. Photomicrograph of old human myocardium (86 years old) taken 

 by its own fluorescence in U.V. light. Bright spots are lipofuscin granules. 

 400X magnification. 



