50 BIOLOGY OF THE PROTOZOA 



the important vital activities including reproduction, and the view 

 has been repeatedly advanced that, for these varied activities at 

 least, two different kinds of chromatin are responsible. One kind, 

 the so-called vegetative or trophochromatin, is active in the ordi- 

 nary metabolic functions of the cell, while the other, the germinal 

 or idiochromatin, has to do solely with perpetuation of the race. 

 While this view of the dual nature of chromatin would seem to be 

 sustained by the phenomena in rhizopods, gregarines, and by the 

 dimorphic nuclei in the ciliates, it is by no means assured that this 

 duality represents a fundamental difference in chromatins. On the 

 contrary it is much more probable, as Hertwig has maintained, that 

 there is only one chromatin and that its functional activity depends 

 upon different factors and conditions which may arise during the 

 life cycle; germinal chromatin in one cell-generation may become 

 vegetative chromatin in the next and vice versa. This is particularly 

 clear in the case of the ciliates where the macronucleus, a distinctly 

 vegetative nucleus, and the reproductive micronucleus, arise as 

 subdivisions of a fertilization nucleus after conjugation or its equiva- 

 lent parthenogenesis. 



The importance of chromatin for life of the cell is indirectly indi- 

 cated by the extreme precision with which it is distributed to 

 daughter cells at the time of division. Like other granules of the 

 cell each chromomere grows and reproduces its exact duplicate by 

 division. Chemically it probably represents the pinnacle of complex 

 structures formed as a result of the activities of constructive meta- 

 bolism while its derivatives, likewise granular in form and difficult 

 to distinguish as chromatin, give rise to many more or less permanent 

 or temporary structures in the cell body, each of which may per- 

 form some cellular activity in its passage through the various stages 

 of chemical breakdown. 



Few investigations of a purely chemical nature have been made 

 on protozoan chromatin. The usual procedure is to designate as 

 chromatin all structures of the nucleus which stain with the so-called 

 nuclear dyes, or to interpret chromatin mainly on a morphological 

 basis. Micro-chemical tests of all protoplasmic substances are made 

 primarily on the basis of solubility or insolubility with acids, alka- 

 lies, salts, etc., and the conclusion that certain structures are made 

 up of certain substances follows from the microscopic picture pre- 

 sented after such treatment. Such tests do not prove that a given 

 structure is composed of a definite substance and is not a mixture 

 of substances. Kossel, Miescher and others have shown that the 

 chromatin bodies composed mainly of the chemical substance 

 nuclein are not dissolved under the action of artificial gastric juice 

 (pepsin and trypsin in appropriate acid and alkaline media) while 

 other portions of the nucleus such as nucleoli and reticulum are 

 entirely dissolved. Chromatin bodies on the other hand are dis- 



