THE AMEKICAN MONTHLY 



[January^ 



in the leaf of Iris pumila ; in other 

 cases it is very minute and some- 

 times cannot be found. Some 

 writers assert that every cell must 

 possess a nucleus during some stage 

 of its growth, but others are in- 

 clined to doubt this. We know but 

 very little about nuclei, and until we 

 have learned much more about their 

 nature and functions, it seems rash to 

 declare that they are essential to the 

 development of a cell ; for we know 

 that in some instances the nucleus 

 does not appear to take any active 

 part in the process of cell-division or 

 multiplication. Still I think it is quite 

 probable that the nucleus always is 

 active when cells undergo division, 

 and it appears, from late researches, 

 that nuclei are present in many cells 

 which have been previously consid- 

 ered to be destitute of them. Owing 

 to the amount of coloring matter in 

 many cells which renders it quite 

 difficult to study the cell-contents to 

 advantage, we are often obliged to re- 

 sort to reagents before we can detect 

 the nuclei. The reagents most common- 

 ly used are such as will stain the nuclei 

 and leave the other structures unco- 

 lored. I have succeeded best with a 

 neutral solution of carmine, but many 

 other staining fluids have been re- 

 commended from time to time. 

 It is not positively known why the 

 nuclei will absorb a color and retain 

 it while the other parts of the cell 

 remained uncolored. In the case of 

 animal-cells it has been suggested 

 that the nuclei possess a slightly acid 

 property after death, which decom- 

 poses the ammoniacal carmine solu- 

 tion and causes the carmine to deposit 

 in them. However, this is purely an 

 hypothesis, and perhaps an unneces- 

 sary one, for nuclei become deeply 

 colored by other dyes than carmine. 

 It appears that they cannot be colored 

 while living, hence the usual course 

 is to kill them first, by plunging the 

 tissue into alcohol, and then apply- 

 ing the staining fluid. 



It is thought that nuclei are por- 

 tions of protoplasm which have be- 



come condensed. Whatever may be 

 their composition or origin, any one 

 who observes them carefully and un- 

 der favorable conditions, cannot fail 

 to have the conviction forced upon 

 him that they are of great im- 

 portance to cells which contain! 

 them. There is often a radiate ar- 

 rangement of the protoplasm about 

 the nucleus, particularly at certain 

 stages of growth, which is quite 

 striking. 



I wish to add a few words about 

 the application of reagents in the 

 study of nuclei. From a chance ob- 

 servation which I made during the 

 Summer of this year, I am inclined 

 to think that very misleading results 

 may be obtained as to the form and 

 position of nuclei, if they are not ex- 

 amined in the living state within the 

 cells. I was applying some reagent to an 

 alga, under the microscope, and just 

 as the fluid reached the cell which 

 was under observation, the nucleus 

 changed its form and appearance to 

 such an extent that I was convinced 

 that the only way to be sure of ac- 

 curacy in this kind of work was to 

 examine the living cells. Nevertheless, 

 the use of certain fluids is necessary 

 in the study of cell-growth — absolute 

 alcohol is one of the most valuable — 

 and when the nuclei are very minute, 

 as in some of the uni-cellular algae, 

 it is necessary to stain them before 

 they can be discovered. 



As my attention will be particularly 

 directed to the functions of nuclei in 

 the cell of algae, I hope to have more 

 to say about this subject before the 

 close of the year. 



The next paper that I intend to 

 present will treat of the processes of 

 cell-division. 



A New Method of Bleaching 

 and Washing Sections. 



Microscopists are indebted to Syl- 

 vester Marsh, for the following ex- 

 cellent process, the description of 

 which first appeared in the English 

 Mechanic. 



