522 C. CLIFFORD DOBELL. 



trausverse section of a cell, passing thvougli the middle of a 

 chamber, Avould present an appearance like that shown 

 diagrammatically in Text-fig. 2 b. The appearance is that of 

 a tube — the wall composed of dense cytoplasm, the inside 

 filled with less dense and more lightly staining cytoplasm. 



Now I think that those individuals Avhich have been 

 exposed to osmic vapour for several minutes and then stained 

 with Giemsa^s stain, present appearances which must be 

 interpreted as representing a structure such as I have just 

 described. The chambered structure of the cytoplasm, with 

 the ring of small granules round the circumference of each 

 partition, is quite clearly seen in these individuals. In optical 

 section, of course, only a single pair of granules is seen — 

 Iving at the point Avhere the partition joins the cell wall. The 

 oranules are of verj^ small size, and are therefore visible 

 under the highest powers only, and after correct differentia- 

 tion. It is difficult to be absolutely certain that a ring of 

 granules is present round each partition, but I believe that 

 this can often be demonstrated. As the bodies of Cristi- 

 spira3 treated in this way remain cylindrical — or undergo 

 only a very slight flattening — in the process of fixing and 

 staining, it is necessary to suppose such an arrangement of 

 the o-ranules to account for their constant appearance at the 

 edo-es of the organism — at the points where the septa and 

 cell- walls unite (cf. figs. 2, 8, etc.). 



As I have pointed out, the organisms which have been fixed 

 by exposure for a shorter time to osmic vapour show pairs of 

 much larger purple granules situated at the points where the 

 partitions join the sides of the cell. A ring of granules is 

 not present in these forms. I believe the correct interpreta- 

 tion of such organisms (figs. 1, 7) is as follows : In the course 

 of making the preparation the organisms have become 

 flattened, as a result of drying following upon inadequate 

 fixation. Exposure to osmic vapour for about half a minute 

 is not sufficient to fix the organisms properly. As they dry 

 on the slide the granules run together into small masses at 

 the edges of the organism, and so give rise to the appear- 



