On the development of the so-called “nuclear fibres,” of the “ elastic fibres,” and of the “ connective tissue.”
Authors: Kölliker A. 
Published: April 2021

ABSTRACT
Elastic Tissue.—The view quite recently propounded by Virchow and Donders, that the so-termed nuclear fibres are developed not from nuclei but from cells, is perfectly correct ; but at the same time I cannot agree with these authors in regarding all the fusiform cells which occur in embryonic connective tissue, and which have been previously variously described, as formative cells of the nuclear fibres, and in their denial of the development of connective tissue from cells. Only the smaller proportion of these fusiform cells have any relation to the nuclear fibres, and they are readily distinguished from the formative cells of connective tissue by their shortness, their dark borders, their fine prolonged extremities, which never form a bundle of fibres, and their elongated, rodlike nucleus. Many of these cells also present, not merely 2, but 3, 6, or more delicate processes, when, without losing their elongated general form, they exhibit the aspect of nucleiform cells. In every situation where nuclear fibres subsequently occur, these cells are met with, in embryos, at four months or even earlier, and, in the tendons, ligaments, and fasciae, still readily admitting of being isolated, in the second half of fœtal life ; and it is extremely easy to show that they form the so-termed “nuclear fibres “and “nuclear fibre reticulated tissue,” by the coalescence of their two or more numerous processes. In very many places, as in the perimysium, the external intiegument, the mucous membranes, fasci§, fibrous membranes, all traces of the original composition from cells is lost, and the so-called nuclear fibres, which I term fine elastic fibres, darstella, the well-known, everywhere uniformly wide, soli’d fasci§ or fibrous reticulations ; whilst in other situations the original enlargements of the cells remain more or less manifest, as occasionally in the fasci§ and ligaments, and especially in the cornea. In these cases a certain relation to the Nutrition of the organs composed of connective tissue, concerned, may be ascribed to the remains of the cell cavities, thougth, at the same time, it appears to me that it is going too far when Virchow at once represents the nuclear fibres as a system of cavities in the connective tissue subservient to nutrition. Moreover the nuclei of their formative cells also take plart in the formation of the nuclear fibres, and indeed frequently not altogether an unessential one, becoming transformed when the cells coalesce into elongated rod-like corpuscles, in the neighbourhood of which the other parts of the cell are occasionally more retracted. What is true of the nuclear fibres applies also to the common elastic tissue. I showed, several years since, that in every situation where elastic tissue exists in the adult, only nuclear fibres are present in the infant at birth ; that consequently these two elementary forntis are connected, and the elastic fibres are developed from a widening out of the nuclear fibres, which holds good also for the elastic and fenestrated membranes, which are nothing but metamorphosed elastic networks. This correspondence in itself is necessarily almost sufficient to show, beyond doubt, then the elastic fibres also proceed from cells ; but that this is the case is also shown by direct observation, in the lig-nuchœ, in the arteries, and the superficial fascia of the abdomen, in Which situations the origin of primarily fine elastic fibres, from fusiform cells, is everywhere pretty easy to be seen. The connective tissue, in its two principal forms—the o 2 close and the lax—is developed in a somewhat different manner. The lax connective tissue, as it occurs for instance in the subcutaneous and submucous tissue, and in the large cavities around the viscera, appears first in the embryo, in the form of a transparent, soft, gelatinous substance. This consists essentially of fusiform, or stellate anastomosing cells, and of a semi-fluid, clear pulp, lodged in the interstices of the cellular network, but contains besides, in the latter, a certain number of rounded cells of no definite character. I first observed this gelatinous connective tissue in the substance which is found between the amnios and the chorion, and at first paid attention only to the anastomosing stellate cells, which I denominated as “reticular connective tissue”