THE ENDOPLASMIC RETICULUM 139 



and re-fed, he noted compact masses of " small vesicles and short tubules ", 

 especially at the periphery of the cell. A subsequent investigation dis- 



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d that this smooth form of the ER undergoes a great hypertrophy in 



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liver cells of rats given the toxic azo dye, 3'-methyl-4-dimethyl aminoazo- 

 benzene [39]. This is a substance which, when fed to these animals, blocks 

 glycogen storage in affected liver cells, and eventually induces liver 

 tumours. In this study it was noted that these prominent developments of 



