INTRODUCTION 47 



a concrete way to throw light on the subject, although much has 

 been written about it. 



Many of the granules found in the cell body of a protozoon as well 

 as those within the nucleus, stain with the usual nuclear dyes and 

 their identification as chromatin is a matter requiring knowledge 

 of their history and fate in the cell. It is only within recent years 

 that an effort has been made to discriminate between the various 

 granules in the Protozoa which stain intensely with the basic stains, 

 and to distinguish the chromatin granules which enter into the make- 

 up of chromosomes from other chromatoid granules which are 

 distributed throughout the cell particularly the chromidia and the 

 \olutin grains. This is the more difficult in Protozoa because 

 chromatin granules are not necessarily confined to the nucleus. 

 p]ven in INIetazoa and plants there are times during division when 

 the chromatin is not confined within a nuclear membrane. In 

 the Protozoa such a condition is permanent in many cases {e. g., 

 in Spirochetes, some flagellates, DUeptus anser, Holosticha, etc.). 

 In other cases the nuclear chromatin, by transfusion or by nuclear 

 fragmentation, spreads more or less widel\' throughout the cell 

 protoplasm (rhizopods, ActinosphcBriiim eichhornii, etc.). Here in 

 different species, the fate of the distributed chromatin varies. 

 In some cases this diffusion of chromatin indicates a degenerative 

 change, the chromatin ultimately losing its characteristic reactions. 

 Thus in ActinosphcBrium eichhornii, Hertwig has showTi that, under 

 adverse conditions such as starvation, or overfeeding, or during 

 periods of depression, such distribution of the nuclear chromatin 

 occurs, the granules ultimately becoming transformed into a 

 characteristic pigment of the cell. In other cases the distributed 

 granules retain their chromatin nature and according to numerous 

 observers are ultimately aggregated into minute secondary nuclei 

 which become the nuclei of conjugating gametes (many types of 

 Rhizopoda and Foraminifera) . In these instances, other chromatin 

 which is retained in the "primary nucleus" takes no part in the 

 germinal activities but degenerates and disappears after the gametes 

 are liberated. It must not be inferred that germinal chromatin is 

 thus distributed in the c^i:oplasm in all cases; on the contrary in 

 the majority of Protozoa the gamete nuclei are derived by division 

 of the morphological nucleus with its contained chromatin, and 

 some authorities, notably Kofoid (1921) deny in toto the origin of 

 gamete nuclei from chromidia. 



^^^lile chromatin thus has a definite germinal function there is 

 equally little doubt of its important participation in the ordinary 

 metabolic activities of the cell. Thus, if an Amoeba proteus or the 

 ciliate Uronychia transfurja (see Fig. 108, p. 226), be cut into two 

 portions one of which contains the nucleus while the other is enu- 

 cleate, the former portion only will digest and assimilate food, grow 



