CHAPTER III 



CYTOPLASMIC INCLUSIONS 

 Ronald F. MacLennan 



All active cells possess a large number of q^toplasmic granules 

 which change in number, size, shape, and composition in accordance 

 with the changes in the activities of the cell of which they are a part/ 



The fact that small granules are so constantly present in the living substance 

 is an indication that such a fine suspension of material represents a colloidal 

 condition favorable for the life process. It seems certain that as the physiology 

 of the cell becomes more clearly understood there will be shown to be a 

 definite dependence of vital phenomena on the granular nature of protoplasm, 

 on the properties which it possesses by virtue of the fact that it is a suspen- 

 sion (Heilbrunn, 1928, p. 20). 



The cytoplasmic granules are a visible part of the fundamental organi- 

 zation of the cell, and the elucidation of their functions contributes not 

 merely to a specialized branch of cytology but contributes directly to a 

 solution of the fundamental problem of protoplasmic organization. 



The richness of the granular complex early attracted the interest of 

 cytologists, and many studies were made on their chemical composition. 

 The report of Biitschli's discovery that the carbohydrate granules of 

 gregarines differ from those in vertebrates is one of the classic papers 

 in the group. During the first thirty years of this century the emphasis 

 shifted from the earlier cytochemical methods to an interest in certain 

 of the granules as permanent, self-perpetuating cytoplasmic organelles, 

 which could be classified by certain empirical reactions such as osmic 

 reduction or the segregation of janus green and neutral red. Dissatisfac- 

 tion with the specificity of these methods has resulted recently in a re- 

 newed emphasis on methods which yield specific information on the 

 chemical and physical nature of the cytoplasmic granules and their 

 cyclic changes. Too often, however, there has been a tendency to carry 



' This paper is a contribution from the departments of Zoology of the State College of 

 Washington and Oberlin College. 



