150 Transactions of the Society. 



to the fact that few cytologists take the trouble to examine care- 

 fully the fixing and staining properties of those bodies which they 

 call " chromidia." Jorgensen (^26), in a paper on the oogenesis of 

 Grantia comj^ressa, calls the mitochondria " chromidia." Dendy (o) 

 has followed Jorgensen, and by both authors the sperm middle 

 piece is called a " chromidium," though it should be noted that 

 these observers were not aware that the body they described was 

 the spermatozoon (see paper (19) ). 



Nearly all cytologists use some form of iron alum hsematoxylin 

 for staining^. While we disas^ree with the statement that such 

 h?ematoxylin stains cannot be relied upon, it is true that these 

 methods tinge a black or grey-blue colour many different cell 

 bodies. To fix a tissue in ordinary Flemming and to stain in iron 

 liaematoxylin, and then to describe in such preparations any blackly 

 stained granule as chromatin or a " chromidium," is unjustifiable ; 

 to describe any cell substances which stain basiphil in the so-called 

 chromatin or nuclear dyes as chromatin is equally unjustifiable, 

 yet perusal of cytological work carried out by many zoologists will 

 show that it is customary to regard basophil materials as chromatin. 

 One example which reminds us of the care which must be taken in 

 the interpretation of cytological staining methods will suffice : 

 methyl green, a dye which is extremely useful for staining chro- 

 matin, will also stain mucin of goblet cells, and the matrix of 

 cartilage ; it is sometimes found that after chrome-osmium fixation 

 pyroniu and methyl green may stain oxyphil materials green, and 

 .basophil ones red. 



It should be noted here that we have no certain methods for 

 differentiating cell chromatin, but there are numbers of ways which 

 enable us to detect and separate out substances which are not 

 chromatin. 



Let us take the case of the so-called sponge-egg " chromidia." 

 After chrome fixation and iron hematoxylin or ironbrazilin stain- 

 ing, these bodies stain black or brownish respectively ; Jorgensen 

 therefore calls them " chromidia." Going somewhat further into 

 the matter, we find that by fixing in chrome osmium and staining 

 in Ehrlich's htematoxylin, the nuclear chromatin goes blue, while 

 the so-called "chromidia" either do not show, or are faintly 

 brownish and not stained; fixing the sponge in Carney's fluid and 

 staining by any other methods fails to reveal the " chromidia " ; 

 fixing and staining by Champy-Kull (JS), the " chromidia '' go red 

 (fuchsin) and the chromatin of the nucleus blue (toluidin blue), 

 while the nucleolus (plasmosome) goes red. Therefore we can 

 pronounce the "chromidia" not to be chromatin, because they are 

 dissolved away by Carnoy, because they fail to stain like chromatin 

 in Ehrlich's ha3matoxylin or by Champy-Kull's method, and 

 because their histo-chemical reactions are those of mitochondria 

 which have no direct relation to chromatin. 



