Anatomists have, over a long period of time, recognised and described thousands of different ‘body parts’ … all of which contribute to the body’s structural form.
Ever since the days of ancient Greece and Rome, Europe’s anatomists have usually focused on describing the parts they can physically see with their naked (unaided) eyesight. This is evidenced in their writing about the body’s membranes, fasciae, aponeuroses, tendons, ligaments, neurovascular sheaths, organ capsules, for instance. The literature they produced shows that that the anatomy profession has, until relatively recently, customarily paid far more attention to describing and discriminating between these macroscopic ‘body parts’ than it has to their minute structure.
They have not, however, neglected it entirely … even in the days before they could use microscopes.
When I began reading my way through a bunch of moderately oldish (18th and 19th century), English-language anatomy textbooks and medical dictionaries – as part of my quest to find out about the ways fascia has been known down through the ages – I was puzzled by the references I repeatedly encountered to something called ‘cellular membrane’. This stuff, which I hadn’t previously heard of, seemed to be interchangeably known by several names – including, for example, ‘cellular tissue,’ ‘cellular texture,’ ‘cellular substance,’ ‘cellular system,’ ‘cribriform body,’ ‘fibro-cellular tissue,’ ‘mucous tissue’ (Adstrum & Nicholson, 2019), ‘adipose membrane,’ and ‘reticular membrane.’
None of this these terms were explicitly defined in the dictionaries and textbooks I looked at, so I had to figure out their meaning from the context in which they were used … and then expand my search outwards from there. It eventually became apparent that all of these now obsolete terms that had something to do with the substance that is now known as ‘soft connective tissue’ or, in some quarters, ‘fascia.’ For instance,
“The Lobe of the Ear is made up of nothing but Skin and cellular substance … [the auditory canal] is lined on the inside by the Skin and cellular Membrane, through its whole length.” (Winslow, 1733, Vol 2, p. 105)
“On the outside of the thigh [the fascia lata] is of great strength and thickness, but at the posterior parts it becomes thinner, and at the inside of the thigh has rather the appearance of cellular substance than of tendinous fascia.” (Simmons, 1780, pp. 420-421)
My research eventually revealed that the European (including English) anatomy profession was, at that time, very interested in describing whatever it was that bodies, and their constituent ‘parts’ (such as organs and muscles) are fundamentally made of (Wilson, 1944). Their naked eye observations showed them that the stuff they were interested in – i.e., its “universal connecting medium” (Simmons, 1780, p. xix) – is spread all through the body, seamlessly condensing into membranes and (denser, stronger) fasciae, amassing between body parts, surrounding nerves and blood vessels, and infiltrating the organs; seamlessly merging from one form to another.
“Cellular texture [tissue] is among the most simple and extensively diffuse of our Solids, not an organ except the Epidermis and Enamel of the Teeth is without it, even the vitrious [sic] humour of the eye is contained in cells of Cellular membrane … The Phosphat [sic] of Lime, the basis of bones is even deposited in cellular membrane.” (Monro, 1794, p. 4)
“Each muscle is surrounded by a very thin covering of cellular membrane, which incloses [sic] it, as it were, like a sheath, and, dipping down into its substance, surrounds the most minute fibres we are able to trace, connecting them to each other, lubricating them by means of the fat which its cells contain in more or less quantity in different subjects, and serving as a support to the blood vessels, lymphatics, and nerves, which are so plentifully distributed through the muscles. This cellular membrane, which in no respects differs from that we find investing and connecting the other parts of the body, has been sometimes mistaken for a membrane peculiar to the muscles; and hence we often find writers giving it the name of propria membrana musculosa.” (Simmons, 1780, p. 243)
Prior to the 19th century development of sufficiently powerful microscopes and the science of histology, anatomists found it difficult to examine and describe this rudimentary substance. Based on what they could see of it, they generally identified it as ‘cellular tissue’ (etc.). It was named for the many tiny open spaces – or cells – within its moist glutinous substance. The anatomists knew that these tiny interstices aren’t actually empty. They were aware that the cells mostly contain “a watery vapour, that is somewhat gelatinous and oily, exhaled out by the arteries and received again into the veins” or, much less often, liquidy fat (Haller, 1754, p. 17). The watery tissue was accordingly identified as ‘cellular membrane’ (or tela cellulosa), and its fat-filled counterpart was alternatively known as ‘adipose membrane (Simmons, 1780; Hooper, 1797). The anatomists had also discovered that the tiny ‘cells’ are connected to each other and communicate over all of the body – which could be seen, for example, in “emphysema” (when the tissue is puffed up with air), and in “anasarca” (an extreme generalised oedema) (Monro, 1754, p. 7).
Without the assistance of microscopes, the minute structure of this substance (which we now think of as ‘areolar or loose connective tissue’) was far from easy to describe. Haller (1754, p. 10) explained that this material made up in part of “simple fibrills” and also partly of “an infinite number of little plates or scales, which, joined in various directions intercept small cells and weblike spaces” An arrangement that enables the body, and its more solid parts, to move freely and amply.
The anatomists of that era somehow deduced that this tissue “is chiefly an animal Jelly” – constituted from a mixture of water and chemicals that are “held together” by the “chemical attraction” between them (Monro, 1974, p. 9). They were also aware that this tissue is interwoven with tiny, cylindrical white fibrils or threads – i.e., Type I collagenous fibres (though they didn’t call them that back then). Cruveilhier (1844, p. 296) later described them as “delicate transparent filaments” that have a “peculiar sinuous or undulating direction”, are “insoluble in cold water”, yet can be “almost entirely converted into gelatine” by “long-continued boiling.”
Nearly 70 years later, Bichat (1822, p. 87) – who, by then was able to use microscopy as a research tool – described this tissue (which he called “the cellular system”) in words that are more familiar to us nowadays. According to him, it is essentially a complex “assemblage of filaments, and of white soft layers, intermixed and interwoven in different ways” leaving open spaces between them that “serve as a reservoir for fat and serum.” This system, he explains, is “everywhere spread, is everywhere continuous.” By then, there was a fair bit of discussion about whether cellular tissue is “essentially a gelatinous material which only on distention assumes the form of filaments and plates, or which takes on these forms at death by coagulation” (Wilson, 1944). In other words, if this substance is primarily fibrous or viscous in nature.
Interestingly, the advent of microscopes and histology led to a change in the way the word ‘cell’ was interpreted. This word was soon used to identify the newly (microscopically) visible little cytoplasm and nucleus-containing cell units – a meaning that persists today. The anatomists, and their histology colleagues, generally shifted their attention to studying this new type of cell, and, until recently (e.g., Benias et al., 2019; Cenaj et al., 2021) have paid relatively much less attention to the body-pervading, amorphous gel substance the cells are intrinsically embedded in.
Also – somewhere between then and now – we somehow seem to have forgotten about something that Haller observed and warned against. Whether, and how much, these cautionary words apply to our 21st century bodies – especially the British ones – has yet to be established!!
“[We] see thence how a weakening of this fabric, by excess of dram-drinking, tea-drinking and lewdness, has reduced the old athletic British constitution of our ancestors to the modern puny [temerity] of habit, obnoxious daily to a train of nervous and other disorders, almost unknown to our progenitors. And these have worse effects on the young, witty, studious and sedentary; who have a natural tenderness of the cellular fabric and nervous system; to [relieve] which, the cortex was timely and happily discovered.” (Haller, 1754, p. 24).
So there, we have been warned!!!