THE AMERICAN MONTHLY 



[January, 



nucleus, protoplasm, or even cell-wall. 

 In the exact language of science, I 

 think the word should be restricted 

 to a structure with cell-wall, proto- 

 plasm and nucleus. Hackel, in his 

 admirable nomenclature, has distin- 

 guished between a cell, which has a 

 nucleus, and a "cytode," which is 

 the same structure without a nu- 

 cleus. 



However, while I would like to give 

 a definite meaning to the word cell in 

 these papers, I am unable to find 

 another word which will convey just 

 the same comprehensive idea of struc- 

 ture, so I must be content to use the 

 word in its very general sense, ap- 

 plying it to structures which may be 

 either living or dead ; and when a 

 more restricted meaning is intended 

 to apply to a living cell with nucleus, 

 protoplasm and cell-wall, the term 

 complete cell will be employed. 



The cell-wall is composed of 

 cellulose. In living cells, when the 

 membrane is very thin, it can be 

 brought into view by causing the 

 fluid contents of the cells to retract 

 from the wall, by allowing a drop of a 

 solution of sugar to flow under the 

 cover-glass. 



Cellulose can be readily detected 

 in the cell-walls by several chemical 

 tests, the best of which is based upon 

 the fact that it is colored blue by 

 iodine, after it has been subjected to 

 the action of certain dehydrating 

 agents,as sulphuric acid or zincic chlo- 

 ride. In applying this test, in any form, 

 it is quite necessary that no excessive 

 quantity of water should be present, 

 for the water would probably dilute 

 the reagent so much that it would 

 not act in a satisfactory manner. 

 The reaction may be obtained in 

 several ways, but the best method is 

 that of Vetillart, which may be briefly 

 given as follows : — 



I. Mix io'='=- of strong glycerin 

 with 5*=*=- of water, in a flask, place 

 the flask in cold water and add, 

 slowly, with constant stirring, i5c-c. 

 of sulphuric acid (of 66°). This mix- 

 ture slowly loses its strength, but it 



can be easily restored by the addi- 

 tion of a little strong sulphuric acid. 



2. Dissolve 5 grms. of potassium 

 iodide in 5o'^'=- of water. 



First treat the specimen to be tested 

 by boiling in a solution of lo parts 

 of sodic carbonate in loo parts of 

 water, then wash out the soda with 

 water, then remove the water as com- 

 pletely as possible by means of blotting 

 paper. Treat now with iodine solution 

 until the tissues are fully impregnated 

 with it, and draw off the excess of 

 the fluid, as before. Then add a few 

 drops of the solution of sulphuric 

 acid. The pure, unaltered cellulose 

 soon becomes colored blue, and where 

 the cell-walls have become changed 

 or lignified, the color is more of a 

 yellowish tint. However, even when 

 the cell-walls have become much 

 thickened and altered, it will be pos- 

 sible to detect the blue color in a 

 thin, inner layer next to the proto- 

 plasm. 



The author of this process considers 

 that the boiling in the soda-solution 

 should not be omitted in doubtful 

 cases. It seems to cause a swelling 

 of the tissues and makes them more 

 permeable to the reagents. Some au- 

 thors recommend, as a substitute for 

 the carbonate, a concentrated solution 

 of caustic potash or soda, with which 

 the specimens should be treated for 

 a few seconds only, but the general 

 employment of such powerful reagents 

 is not to be advised. It is claimed, 

 however, that the blue reaction has 

 been obtained in certain tissues after 

 treating them with caustic alkalies, 

 while they failed to give the result when 

 the carbonate was used. It should 

 be observed that the blue color is 

 not permanent — it soon disappears. 

 In my own experience I have found 

 no difficulty in obtaining a good blue 

 coloration without the use of any al- 

 kaline solution, but there is no doubt 

 that it is always best to carry out the 

 directions of Mr. Vetillart. In my 

 hands a concentrated solution of zin- 

 cic chloride, containing a little potas- 

 sic iodide and iodine has invariably 



