THE CYTOPLASM 205 



the largest unicellular organisms. Definitive cytochemical data have been 

 obtained, however, from the fragments of these cells, the conclusions being 

 dependent upon correlations between the amount of enzymic activity and 

 the presence of a given cell structure in an isolated fragment.'* According 

 to recent reviews,*'^^ the accomplishments in this field are limited to cor- 

 relations demonstrating the localization of amylase,'* proteinase,'* and 

 succinic dehydrogenase*" in the mitochondria of amoebas. Although it is 

 obvious that the results obtained with the submicrotechnics are not very 

 extensive, the data have been invaluable in that they have provided in- 

 dependent confirmation of certain findings obtained with other cytochemi- 

 cal methods, notably that of cell fractionation. 



4. The Cell Fractionation Technic 

 a. Advantages and Limitations 



In the technic of cell fractionation, the cells of a tissue are mechanically 

 disrupted, and the nuclei, mitochondria, and other cellular components 

 are released into a suitable medium from which they can be isolated by 

 differential centrifugation. This method has the advantage of permitting 

 the isolation of all the particulate components of cells from a single sample 

 of tissue in a yield and degree of purity sufficient to permit an accurate 

 comparison of the properties of the isolated structures. Furthermore, the 

 fact that the cell fractions can be obtained in almost unlimited quantities 

 makes it possible to utilize accepted analytical methods in studies of the 

 biochemical properties of the isolated cell components and thus to keep 

 pace with the rapid advances in biochemistry. It is obvious, therefore, 

 that the cell fractionation procedure is capable of yielding more informa- 

 tion about the properties of cell structures than is any of the other cyto- 

 chemical methods available. For this reason, it is extremely important to 

 define the limitations of the technic. It is necessary first of all to recognize 

 that the tissues commonly used for the isolation of cell structures do not 

 represent uniform populations of a single cell type. Thus, although mam- 

 malian liver consists predominantly of hepatic parenchymal cells (85 to 

 80 % by volume) , 40 to 50 % of the total number of cells are nonparenchymal 

 in type.*^ Since it is therefore apparent that the nonparenchymal cells 



'* H. Holter and W. L. Doyle, Compt. rend. trav. lab. Carlsberg, Ser. chim. 22, 219 



(1938). 

 ^* H. Holter and S. L0vtrup, Compt. rend. trav. lab. Carlsberg, Ser. chim. 27, 27 



(1949). 

 ■*" N. Andresen, F. Engel, and H. Holter, Compt. rend. lab. Carlsberg, Ser. chim. 27, 



408 (1951). 

 " M. E. Wilson, R. E. Stowell, H. O. Yokoyama, and K. K. Tsuboi, Cancer Research 



13, 86 (1953). 



