Bauhaus-Universität Weimar

106 
DEVELOPMENT OP THE TISSUES. 
separately in the gummy fluid, have attained their full size, the 
formation of the cell commences.(a)* 
Modern vegetable Physiologists had already arrived at the result 
that the different tissues of plants, such as cellular tissue, woody 
fibre, ducts and spiral vessels are all originally developed from cells. 
The mode of formation of these cells has been explained by Schlei- 
den.t He has shown that they are produced from the “ nuclei” of 
Robert Brown, and hence he calls these bodies “cytoblasts” [xvtos 
a cell, ß-Kaatos a germen]. The cytoblast is generally of a yellowish 
colour, and internally of a granular structure. In its interior Schleiden 
has detected a second nucleus (nucleolus) called by him the nucleus 
corpuscule, which sometimes resembles a mere spot, at other times 
a hollow globule. The cytoblasts are developed in a mass of mucous 
'granules contained within previously existing cells. As soon as 
they have attained their full size, a delicate transparent vesicle rises 
upon the surface of each. This is the young cell, which at first bears 
the same relation to the flat nucleus as the watch-glass bears to a 
watch. When the cell has increased in size the cytoblast appears 
merely as a solid body included in the wall of the cell. The layer 
which now covers the cytoblast on the side towards the interior of 
the cell is extremely delicate,—indeed, seldom to be recognised by 
the eye,—and it soon becomes wholly absorbed, while the cytoblast 
itself disappears at the same time. The newly developed cells lie 
free in the cavity of the parent cell, and, as they grow and exert 
reciprocal pressure against each other, assume the polyhedral form. 
The following are the more important observations of Schwanni 
respecting the cells of animals and the agreement of animals and 
plants in their ultimate structure. 
In the chorda dorsalis, the cellular structure of which I had myself 
pointed out long since, Schwann first discovered the nuclei or cyto¬ 
blasts. Each cell of the chorda dorsalis of Pelobates fuscus has its 
disk-like cytoblast lying at the inner surface of the wall of the cell; 
and in this nucleus there is seen one, rarely two or three, clearly de¬ 
fined spots. In the cavity of the cells young cells are developed, as 
in plants. 
Cartilages also are, according to Schwann’s observations, com¬ 
posed entirely of cells, when first formed. The cartilaginous bran¬ 
chial rays of fishes at their apex are composed of small polyhedral 
cells, lying in close contact with each other, and having very thin 
(a) The preceding paragraph and the whole arrangement of this Book, together 
with pages 97-8 from Liebig, are introduced by the American editor, who believes 
that a view of the formation, distribution, and general properties of the tissues, 
ought to precede an inquiry into the functions of the several organs, which are in 
various proportions composed of these tissues. 
* Brit. & For. Med. Rev. Vol. IX. 
*' Müller’s Archiv. 1838, p. 137. 
£ Froriep’s Notizen, 1828, No. 91, 102, 112. Schwann, Mikroscopische Unter¬ 
suchungen über die Ueber-einstimmung in der Structur und dem Wachsthum der 
lhiere und Pflanzen, Berlin, 1838. A review of this work wüth a copious ab¬ 
stract of its contents is contained in the 9th volume of the British and Foreign 
Medical Review.
        

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