CHAP, i The Cell 179 



the observations and teaching of Hertwig, Strasburger, 

 Kolliker, and Weismann. 



For many years after its discovery its general substance 

 was considered to be quite distinct from the general sub- 

 stance of the cell, and the early theories of protoplasm did 

 not include it. It was not till 1882 that we find its true 

 relations taught, when Strasburger included it in the proto- 

 plasm of the cell, which he spoke of as differentiated into 

 cytoplasm and nucleoplasm. 



The universal occurrence of the nucleus as an integral 

 part of the protoplasm of the cell was not at once admitted. 

 The researches of Schmitz carried out in 1879 an( ^ *88o 

 established its existence in many of the lower Thallophyta, 

 including Yeast. Schmitz was inclined to deny its presence 

 in the Cyanophyceae and the Bacteria. A body corre- 

 sponding to the nucleus, though not possessing the same 

 complicated structure, was found in both these groups 

 independently by Wager and by Zacharias (1890-95). 



The researches into the nature of the nucleus, like those 

 relating to the structure of the protoplasm, were conducted 

 by biologists upon both animal and vegetable tissues, with 

 the result that demonstration was forthcoming of the 

 practical identity of the nuclear as well as the cell proto- 

 plasm in the animal and vegetable kingdoms. It is difficult 

 therefore to discuss the progress of knowledge from the 

 point of view of the latter only. The work of the two 

 schools of research is in this case mutually supplementary, 

 the leading facts having been supported by both. 



The first satisfactory account of the structure of the 

 resting nucleus was derived from the researches of Schmitz, 

 Strasburger, and Flemming, conducted independently in the 

 years 1879 and 1880. According to these investigations 

 it consists of a homogeneous ground substance, sometimes, 

 however, having a finely dotted appearance, in which a 

 more solid material is present in the form of a reticulum 



M 2 



