IN VIVO FUNCTION OF SUBCKLLl'LAK PARTICLKS 5 



reticulum of Porter aiul Paladc (42) may be used as idenlilying markers (27, 28). 



Figure 4 is a section through a microsome fraction from the same homogenate. 

 The manner in which the ergastoplasm is fragmented is not yet understood. 

 Generally, the fragments are quite short, as in this figure. Sometimes, as in the 

 so-called 'fluffy layer,' they may be surprisingly long (fig. 5). 



That the microsome fraction, even in liver, contains other cytological entities 

 is well recognized. In our laboratory, we are trying to determine the extent to 

 which the so-called 'smooth membranes' seen in the microsome fraction are 

 derived from the microvilli on the surface of the liver cell. These microvilli may 

 be of considerable enzymatic importance, as we shall see later, and they are 

 extremely numerous. 



Figure 6 is a section of liver demonstrating the microvilli on the cell surface 

 exposed to the blood sinusoid (space of Disse). The area thus exposed to the 

 blood (plasma?) is very large, and it is covered by literally millions of these tiny 

 extensions of the plasma membrane. We do not know how many micro\illi sur- 

 vive homogenization and how many are centrifuged into the microsome fraction. 



Figure 6 also shows numerous structures near the sinusoidal surfaces which 

 resemble pinocytosis vacuoles. Such vacuoles are seen in electron micrographs of 

 other tissues and appear most numerous in capillary endothelium (25). 



Microvilli are also present over other areas of the hepatic cell, those exposed 

 to the bile canaliculi (fig. 7). As we suggest later, the enzymatic nature of these 

 microvilli may differ from that of Disse space microvilli. Some of the canalicular 

 microvilli sediment into the nuclear fraction, as part of the bile canaliculus 

 fragments (33, 34). It would not surprise us if others end in the microsome 

 fraction. 



The section shown in figure 7 passes through a structure with a long, stormy 

 history, the Golgi apparatus. The reality of this organelle can no longer reason- 

 ably be questioned, thanks to electron microscopy. Elsewhere in this volume. 

 Dr. KufT (21) discusses some chemical properties of the Golgi apparatus isolated 

 from epididymis. An excellent review of the Golgi apparatus, by Dr. Palay, has 

 just appeared (39)- 



From electron micrographs it is difficult to sense what is readily apparent in 

 the thicker sections used for light microscopy, narnely that in liver parenchymatous 

 cells the Golgi apparatus is a multiple structure, arranged on either side of the 

 bile canaliculi along their entire length (fig. 9; also (34)). 



Figure 7 also shows the peribiliary 'dense bodies,' structures of current interest 

 because they may be the lysosomes postulated by de Duve and colleagues. Dr. de 

 Duve refers to the 'dense bodies' when he discusses this important concept of 

 lysosomes later in this \c)lume (8). 



Because electron microscopists frecjuently try to reconstruct processes from 

 static photographs, and because everything is yet so novel, there is a great tempta- 



