670 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Some of the cellular elements of the tissues have been noted with 
even simple Microscopes for over two hundred years. Dr. Hooke, in the 
year 1665, being among the first observers. The nucleus itself may be 
said to have been seen and described over one hundred years ago. It is 
still, however, true that the first great step leading to actual scientific 
advancement in this subject was made in 1831 by the distinguished 
botanist Robert Brown. He gave us definite knowledge of vegetable cells, 
and he demonstrated that the nucleus was a normal element of the cell. 
What was called the nucleolus was discovered by Valentin five years 
later. 
But even before Brown, Turpin had affirmed tbe physiological 
significance of the cell, attributing to cells distinct individualities, and 
affirming generally that plants were formed by their agglomeration. 
But, as is now well known, the cell theory proper was founded by 
Schleiden, but by him it was restricted to plants. He defines the 
vegetable cell as “ the elementary organ which constitutes the sole essen- 
tial form-element of all plants, and without which a plant cannot exist ; 
and as consisting, when fully developed, of a cell-wall composed of 
cellulose, lined with a semi-fluid nitrogenous coating.” 
To him, therefore, the cell presented itself as a vesicle with semi-fluid 
contents. This was in 1838. In the following year Schwann extended 
the cell to the animal kingdom, but to the two elements of Schleiden he 
added a third, that is to say, the nucleus, which he deemed essential to 
the existence of the cell in some period of its history. And on his 
authority these triple elements of the cell were universally believed to 
exist. 
In proportion, however, as the cell theory was more and more exten- 
sively seen to characterize the animal world, it was found increasingly 
difficult to maintain the threefold constituents of the cell. 
The conception that the cell was a “ vesicle closed by a solid 
membrane containing a liquid in which floats a nucleus containing a 
nucleolus ” rapidly gave way before investigation. In 1811 it was 
shown that cells multiplied by budding, and that the nucleus underwent 
fission when the cell divided ; and it was contended by Goodsir that no 
cell could arise save from a parent cell, which was seen by Virchow to 
have direct application to pathology. 
But it was Naegeli, a botanist, who showed first the unimportance of 
the cell-wall, and he was supported by Alexander Braun. But it was 
scarcely a universally accepted belief until Leydig, in 1857, decidedly 
declared it unessential, and defined a cell as “ a soft substance inclosing 
a nucleus.” 
After this it was shown by Max Schuitze that a cellular life might 
be complete even without a nucleus, as in Amoeba porrecta ; thus we 
come back to the cell as the ultimate morphological unit in which there 
is any manifestation of life. 
Thus, then, by the cell theory in this form we discover that “ every 
animal presents itself as a sum of vital unities, any one of which 
manifests all the characteristics of life.” 
I must not linger even for a recapitulation of the earlier views held 
regarding the living matter which constituted the cell ; enough here that 
it was held to be a matter with an endowment of its own, possessing 
