456 C. C. MACKLIN. 



nucleolar material (Fig. 24). Occasionally two fragments would 

 be found in one nuclear part while the other had none; again 

 ,it was very frequently found indeed it w T as the rule that a 

 nucleus would have two separate nucleolar fragments without 

 any nuclear division. In short not only was the division of the 

 nucleolus in most cases not followed by nuclear fission, but the 

 latter took place in many cases without division of the nucleolus. 



Neither before nor after nuclear fission was there discovered an 

 instance of differential staining of the two halves of a nucleus 

 about to be divided, or already divided, as shown by Child ('07) 

 so that there was no evidence of this kind to support the belief 

 of Child that there may be a physiological independence of the 

 nuclear areas even before they become amitotically divided, 

 manifested by a variation in the staining of the two nuclear 

 halves. The study of living nuclei, too, divulged nothing in 

 favor of this hypothesis. 



The result of this process of nuclear splitting was the formation 

 of a cell containing one or more separate nuclei of about equal 

 size, and each of about the same size as the nuclei of mononu- 

 cleate cells. After nuclear fission the separated nuclear elements 

 manifested the power of growth, and seemed to have metabolic 

 independence. The cell protoplasm also of these cells shows an 

 ability to increase in bulk. This is especially evident in giant 

 cells which can thus become quite large. 



It is believed, furthermore, that binucleate cells and giant 

 cells in tissue cultures (except foreign body giant cells which 

 arise by fusion of previously separate cells) do not arise in any 

 other manner than that above outlined, for there is no other 

 adequate explanation of their origin. A careful examination of 

 living and fixed material does not reveal any evidence of fusion 

 of cytoplasm without fusion of the nuclei, so that there are no 

 grounds for admitting this as a possible theory of formation. 

 Although many of the binucleate cells undoubtedly do migrate 

 as such from the original piece, w r here they are doubtless formed 

 in the same manner as they are in the new growth, yet an increase 

 of over 100 per cent, in their number in the growth of the second 

 day as compared with that of the first (as ascertained by making 

 careful counts of the 20 heart specimens aforementioned) can 



