NUCLEAR DIVISIONS IN AMOEBA 41 



study the phenonu'iion in ' fixed ' specimens a fairly large 

 number of young amoebae should be placed on a slide in 

 a small drop of water and left in a damp chamber until the 

 animals begin to creep about on the glass. The fixative should 

 then be dropped quickly on to them, when, a cover-slip having 

 been provided, they can be examined microscopically (aceto- 

 carmine is very useful for this purpose) and the whole range of 

 positions studied. (The behaviour of a nucleus in a living 

 amoeba is highly reminiscent of the tossing of a pancake on 

 Shrove Tuesday !) 



For the purpose of this investigation, in addition to an 

 unlimited supply of hving amoebae for examination and of 

 specimens treated with aceto-carmine, whole cultures were 

 fixed in corrosive alcohol, in warmed corrosive acetic, and 

 stained in Delafield's haematoxylin, carmine,^ light green, etc., 

 and the individual nuclei studied whole or sectioned. I am 

 greatly indebted to Sister Carmela Hayes for much assistance 

 in making preparations. 



In stained preparations the ' resting ' nucleus is a much more 

 striking object when seen with the karyosome in elevation 

 than it is when the latter is viewed in plan. A newly formed 

 daughter nucleus can easily be picked out from a number of 

 older nuclei by the more brilliant colouring exhibited by the 

 karyosome, especially in aceto-carmine preparations. 



Doflein states that the division of the nucleus is effected 

 when the amoebae have temporarily drawn in their pseudo- 

 podia and have assumed a spherical shape, having freed them- 

 selves from the substratum. They look extremely opaque in 

 this condition. It is a common sight to see several of these 

 opaque-looking spheres in any good culture of amoeba. In 

 one instance, Sister Carmela, who was tending the cultures 

 during my absence, reported to me that practically every 

 amoeba in a particular culture (and there must have been 

 many thousands) had rolled itself into a ball.^ 



^ A modified formula of Picro-magiiesia-Carmiiie suggested to me by 

 Dr. J. S. Dunkerly was also applied. 



^ The subsequent history of this culture, which shortly afterwards 



