ox CKISTISPIKA VENERIS XOV. SPEC. 531 



i-ise to a less precise staining of the cell as a whole. Cristi- 

 spii-a3 which have been subjected to osmic vapour for many 

 minutes tend to take up a more diffuse blue stain, and show 

 the chambered structure less distinctly in consequence. But 

 althouo-h this is the case, the chambers can always be seen. 

 They never disappear completely, though they do become 

 fainter after more prolonged fixation. That the chambered 

 structure cannot be seen in the living organism I do not 

 regard as any proof of its non-existence. For the width 

 of the cell is small (less than 2 /x) : the cell-membrane is fairly 

 thick and possesses a considerable degree of refractivity : 

 and the difference in refractivity between the protoplasm 

 forming the walls of the chambers and that which tills them 

 is probably not very great in the living organism. The 

 chambered structure appears with such constancy in organ- 

 isms fixed with osmic acid or corrosive sublimate that it will 

 i-equire a good deal more evidence than that furnished by 

 Gross to prove that it does not exist. 



Swellengrebel's (1907) original account of C. balbianii 

 differs iu some ways from his later description (1909), in 

 which he records appearances which are consistent with my 

 interpretations. The transverse bars of chromatin which he 

 describes are, I believe, similar to the transverse bars which 

 I have frequently seen, and are produced in precisely the 

 same way — by imperfect fixation. Swellengrebel states that 

 he fixed the organisms in formaldehyde (1907, p. 19), but he 

 appears to have overlooked the fact that fixation in tlie way 

 he describes is inadequate unless employed in conjunction 

 with after-treatment with alcohol — a point Avhich I have 

 already had occasion to point out elsewhere (Dobell. 1910aj. 



It is apparent from the foregoing, therefore, that whereas 

 Schellack appears to regard the body of a Cristispira as 

 being chiefly composed of a nuclear structure, Gross regards 

 it as enucleate, and I regard the nucleus as being in all 

 probability represented by chromidial structures arranged in 

 the manner described in previous pages (see p. 521). 



Plasmolysis. — Swellengrebel (1909) has proved that 



