exhibited a variety of shapes, and ranged in size from 0.25// to 0.50//. 

 Many of the particles possessed numerous electron-dense granules, a 

 distinct internal cavity, and were bounded by an external limiting mem- 

 brane. Electron micrographs of liver sections showed the dense bodies 

 to be mosdy localized along the bile canaliculi of the parenchymatous 

 cells. This intracellular distribution corresponds to that of acid phospha- 

 tase, which previously had been demonstrated by Holt (1954) to be 

 essentially localized along the bile canaliculi in association with specific 

 granules. On the basis of these observations, it would appear that the 

 pericanicular dense bodies correspond to the acid phosphatase-contain- 

 ing granules associated with the bile canaliculi and represent the lyso- 

 somes, at least in terms of this particular enzyme (deDuve, 1959, 

 1960). 



Polymorphic bodies corresponding morphologically with the dense 

 bodies and located adjacent to the bile canaliculi have been observed by 

 Rouiller (1954) and Palade and Siekevitz (1956) in electron micro- 

 graphs of parenchymatous cells of mammalian liver. Also the so-called 

 "microbodies" described by Rouiller and Bernhard (1956) in regener- 

 ating liver cells, and suggested by these workers as possible precursors 

 of the mitochondria, may be identifiable with the dense bodies described 

 by Novikoff and group (deDuve, 1959). Recently, Beaufay and co- 

 workers ( 1 959 ) have achieved fractionation of the lysosome-rich frac- 

 tion into two biochemical components: one containing the typical 

 lysosomal hydrolases (acid phosphatase, ribonuclease, /^-glucuronidase, 

 etc.); the other containing uricase, catalase, and D-amino acid oxidase. 

 This differential separation of two distinct groups of hydrolases suggests 

 that each enzyme group probably operates as a unit and is associated 

 with a specific type of particle (Beaufay, et ciL, 1959). Electron micros- 

 copy studies of Beaufay (unpublished) on purified preparations of lyso- 

 somes from rat liver have demonstrated the existence of two distinct 

 types of particles associated with this fraction (Figure 3-20 (a) and 

 (b)). One morphological component is represented by the pericanicular 

 dense bodies or true lysosomes. The other component, the so-called 

 "microbodies," differs from the pericanicular dense bodies by the pres- 

 ence of a lamellar or crystalloid core. Whether or not the microbodies 

 represent the subcellular particles with which the hydrolases — uricase, 

 catalase, and D-amino acid oxidase — are associated, remains to be deter- 

 mined (deDuve, 1960). 



Available evidence suggests that the lysosomes may be involved in 

 intracellular digestive activities such as phagocytosis and pinocytosis. It 

 has also been suggested that a relationship may possibly exist between 



STRUCTURE AND FUNCTION OF CYTOPLASMIC ORGANELLES / 47 



