194 INTRODUCTION TO CYTOLOGY 



position at the center of developing spores recalled the behavior of nuclei 

 elsewhere. 



That certain bacteria may contain definite nuclei in spite of the above 

 uncertainties has been rendered more probable by the recent work of 

 Stoughton (1929) on Bacterium (Pseudomonas) malvacearum. By 

 employing the methods of Enderlein (1925) and Nakanishi (1901), in 

 which obscuring nutritive materials are removed and the cells are stained 

 without drying, this investigator has been able to differentiate a central 

 body about 0.5^1 in diameter which shows an affinity for basic dyes and 

 passes through a definite division cycle correlated with that of the cell. 

 In some cases this central body elongates and becomes divided with the 

 cell as the latter constricts, w^hile in others it becomes dumb-bell shaped 

 and completes its division before the cell divides by forming a transverse 

 wall. It can be seen in living cells under dark-field illumination. It is 

 Stoughton's conclusion that this central body is in all probability either a 

 nucleus or possibly (following Enderlein's theory) a nucleus imbedded in a 

 mass of chromatic food-reserve substance. Appearances very suggestive 

 of nuclear fusion and division have been reported for the avian tubercle 

 bacillus (Lindegren and Mellon, 1932). 



Chromidia. — In 1902 R. Hertwig described in Actinospharium and 

 certain other rhizopods what appeared to be an emission of chromatic 

 granules from the nucleus into the cytoplasm. The nucleus might even 

 break up completely into such granules. He called these granules 

 chromidia and set forth a "chromidia hypothesis." According to those 

 who developed this hypothesis, ^^ there are in an ordinary nucleus two 

 kinds of "chromatin": idiochromatin, concerned in reproduction; and 

 trophochromatin, concerned in nutrition. The chromidia are granules 

 of trophochromatin which pass into the cytoplasm where they degenerate 

 (Hertwig) or play a role in the differentiation of specialized structures 

 (Goldschmidt). In certain rhizopods they may consist of idiochromatin 

 and give rise to gamete nuclei. It was further suggested that in the 

 infusoria the micronucleus contains the idiochromatin and the macro- 

 nucleus the trophochromatin, and that the ordinary nucleus of higher 

 forms is thus a duplex "amphinucleus." This " binuclearity hypothesis" 

 has now fallen into disfavor. 



Chromidia were described in many animal tissues by other investi- 

 gators, ^° some of whom did not, however, subscribe to the above views 

 regarding their origin and significance. They were particularly con- 

 spicuous in oocytes and spermatocytes, where a mass of them developed 



34 R. Hertwig (1902, 1904), Goldschmidt (1904 et seq.), Goldschmidt and Popoff 

 (1907), Popoff (1906 et seq.), Schaudinn (1903), Schaxel (1910 et seq.). 



^' Marcus (1907), Wassilief (1907), Reichenow (1908), Nowikoff (1909), Buchner 

 (1909), Moroff (1909, 1911), M. Jorgensen (1910, 1913), Nussbaum (1913), Hirschler 

 (1913), van Herwerden (1913). 



