BERNARD L. STREHLER 379 



The opposite extreme in cell types is illustrated in Figure 3 

 which shows a section from old human myocardium. These cells, 

 in contrast to skin cells, do not die regularly, but rather live for the 

 lifetime of the animal. A most interesting feature of such cells is the 

 fact that they accumulate a fluorescent brown pigment known as 

 lipofuscin ( 17 ) . We are attempting to isolate and characterize this 

 substance. The fluorescent component appears to be an auto- 

 oxidized, unsaturated lipid. We have shown that this material accu- 

 mulates linearly with time (32), at the rate of about three-tenths 

 percent of the total heart volume per decade. Gedigk and Bontke 

 ( 14 ) have demonstrated that these granules possess a number of lytic 

 enzymes and may thus be a type of lysosome. Lipofuscin apparently 

 accumulates in all non-dividing cell lines. On the other hand, it 

 does not generally appear in dividing cell lines. I would like to 

 suggest that the heart is analogous to Campamdaria and that there 

 exists an analogy between anemones or hydra and the regularly 

 replenishing structure, skin. In the former case, there is no regular 

 cell replacement since the cells of the nervous system and the heart 

 are carried through the life of the individual. On the other hand, 

 the skin is in a continual process of replacement just as is hydra 

 with its growth in the hypostomal region and the death of cells at 

 the base and probably at the ends of the tentacles. 



In support of this thesis, I would like to concentrate on a com- 

 parison between certain histochemical properties of H. littoralis and 

 Cajnpannhria which are being studied in cooperation with Dr. 

 Mary Anne Brock (6). In Figure 4 is illustrated the regression 

 process in Campamdaria as recorded in time lapse movies. Campa- 

 nularia exhibits regular peristalsis very much as does Cordylor- 

 phora. The histological appearance of a young Campanularia is 

 shown in Figure 5. 



The first sign of the senescence of the individual hydranth is a 

 slight shortening of the tentacles and the appearance of knobbiness 

 accompanied by a change in refractive index on the end of them. 

 The tentacles then begin slowly to shorten and draw in toward 

 their bases. After the tentacles have contracted completely, there 

 is a sudden release of something which breaks down the intercellular 

 cement and, at the same time, results in cell autolysis. A hydranth 

 in this stage is shown in Figure 6. Finally, the entire contents of the 



