328 



NATURE 



\Aug. 20, 1874 



it acts continually in obedience to the first great law ; it increases 

 and multiplies, and replenishes the earth. 



Let us now for a few moments compare our former views of 

 the structure of animal membranes with the present ones. The 

 skin (covering the outer surface of the body), the mucous mem- 

 branes, the serous hnings of the great internal cavities and of the 

 blood- and lymph-vesscIs, and tbe lining membranes of joints 

 were all alike viewed as il formed of a delmite membrane covered 

 on one side by cells, and on the other supplied by blood- and 

 lymph-vessels and by nerves — the membrane covering in the 

 latter parts and affectmg an absolute separation of the cells Irom 

 the vessels and nerves, which were universally believed never to 

 penetrate into the cellular layer. The cells were regarded as the 

 parts actively engaged in the performance of the lunctions, the 

 vessels and nerves aiding thereto supplying materials to be acted 

 on by the cells, and the nerves regulating the amount of action 

 at particular tmies for special purposes. The diseased condi- 

 tions, like the functions, %\ere kept perfectly distinct ; and we 

 had one set of diseases of the epithelial or cellular parts, and 

 another and a ditfcrent set of diseases of the membranes and of 

 the parts below. 



1 thmk the first occasion on which the public failh in these 

 views was seriously shaken was when the laie distinguished I'ro- 

 fessor of Medicine in St. Andrew's, Dr. John Reid, died of what 

 was called an epithelial cancer of the tongue. Microscopical 

 examinations showed that the disease existed in the cellular 

 covering ot the tongue. A sufficient cause for it was supposed to 

 exist in the irritation caused by sharp points of the teeth, to 

 cover which a protecting silver plate was constructed. The 

 diseased parts were remo\-ed with the greatest skill and care by 

 Su- Wiliiaar Fergusson, and subsequently by the late Dr. James 

 Duncan, assisted by Mr. Goodsir and Mr. Spence, now Professor 

 of Surgery in the University of Edinburgh. Every conceivable 

 care was taken by these attached friends of the poor sufferer to 

 remove every trace of the disease ; but it progressed steadily and 

 destroyed his valuable lile. 



At this period no one could understand the extension of an 

 epithelial disease through a basement membrane ; and therefore 

 the affection of the adjacent lymphatic glands was explained by 

 supposing the diseased action to have been propagated from cell 

 to cell along the epithelial surface of the lymphitic vessels. 



Not long alterwards the sternly trathlul and accurate Sir 

 James Paget declared, in terms of terrible significance, to the 

 sufferers Irom this disease, that epithelial cancer takes a little 

 longer time than ordinary cancer to do its fatal work. 



And it soon became tlioroujhly well known that the glands of 

 the skin, the hair-bulbs, and the teeth are produced by a local 

 development of the deep cells of the cuticle, extending lar below 

 the line ol the basement membrane or cutis, and through the 

 position which it was supposed to occupy, as though no mem- 

 brane were there to hiiiuer them. 



Thus the basement membrane, which was supposed so arbi- 

 trarily to separate the cells on one surlace of membranes irom 

 the vessels and nerves on the other, gives way at once belore an 

 increased development of the cells, whether in the ;orination ol 

 new organs or the exttnsion of disease. And the membranous 

 walls 01 capillary blood-vessels allow the corpuscles of the blood 

 to pass through them much in the same way as solid particles 

 enter into ana traverse the substance of the protoplasm ol an 

 amceba or other mass of sarcode. 



Whilst physiologists were engaged in these observations, the 

 late Master of the Mint, Mr. Graham, was conducting a series of 

 experiments of the most remarkable kind, and ol the utmost 

 iniportance to physiology as well as to cheniisiry and physics. 

 He lound it necessary to separate the two sets of substances as 

 crystalloids and colloids, — the colloids being penetrable by the 

 crystalloids as readily as water, the crystalioios (such as hydro- 

 chloric acid and common salt) passing through organic mem- 

 branes with great freedom, whilst many of the colloids, such as 

 albumen ana gum, will not penetrate them at all. This dis- 

 covery has enabled the chemist to separate crystalloids from 

 colloids by dialysis, even when they occur in the most minute 

 proportions — (or instance, to separate So or 90 [Jcr cent, of a 

 ten-thousandth part of arsenious acid in twenty-lour hours from 

 porter, milk, or infusions of viscera, substances notoriously 

 diflicuit to analyse. And it has enabled physiologists to explain 

 how animal membranes are traversed by various substances 

 which couUl not pass through them without being changed irom 

 the colloidal into the crystalloidal form. Thus the colloidal starch 

 and albumen of our foui.1 scarcely admit of absorption until in 



the process of digestion the starch becomes sugar and the albu- 

 men albuminose, crystalloidal bodies which pass through 

 animal membranes with great facility. And again, this crystal- 

 loidal albuminose, alter having passed into the tissues through 

 the membranous walls of the vessels, may become a second time 

 a colloid, and be deposited and fixed as tissue-substance, ready 

 in its turn to be permeated by crystalloids either for temporary or 

 more durable purposes in the economy. 



The eltect of this great discovery 01 Mr. Graham's shows how 

 impossible is the advance of physiology without a corresponding 

 advance in our knowledge of chemistry and physics. 



If basement membranes, the walls of blood-vessels, and of 

 cells are made up of colloidal maiter, we can easily understand 

 how they are penetrated by crystalloids ; and in like mannei it 

 is perfectly possible that they may be traversed by other sub- 

 stances in solid forms — as, for instance, the walls of blood-vessels 

 by the corpuscles of the blood. No wonder that there is a con- 

 tinual deposition and removal of the constituents of the 

 tissues, if so slight a change as that from the crystalloidal to the 

 colloidal form, and the leverse, makes such perlectly marvellous 

 differences in the relations of these substances to each other. 



We must look upon the tissues of an animal body as we do 

 upon the substance of an amceba, and recollect how penetrable 

 the surfaces and tissues of animals are ; then we shall cease to be 

 startled when we see these parts become the seat of entirely new 

 deposits, or find them traversed by migrating blood-corpuscles 

 as freely as a colloid is penetrated by a crystalloid. 



It is impossible to foresee what may be the result to physio- 

 logy of this great advance in our knowledge of the varying rela- 

 tions ot substances to each other according as they present them- 

 selves at different times in the opposite physical conditions which 

 were described by Mr. Graham as crystalloidal and colloidal. 

 Uut it is plain that we cannot continue to look upon animal 

 membianes as forming such decided barriers against the penetra- 

 tion of one tissue by another, or by foreign matters, as was once 

 supposed. 



J^et me now direct your attention to the present aspect of the 

 question how far basement membranes limit the distribution 

 of vessels and nerves, and separate them from the cells of glands 

 and membranes. 



Mr. Bowman, in his admirable researches into the anatomy 

 of the organs of sense, discovered that the filaments of the 

 nerves ol smell have a remarkable structure — that they are 

 nucleated, finely granular, contain no white substance ol Schwann, 

 and resemble the gelatinous nerve-fibres. The epithelial surface, 

 too, of the olfactory region Mr. iJowman descrioed as differing 

 greatly from that ot the adjacent parts of the nasal mucous mem- 

 brane, and as being o( a dark sepia tint. Subsequent exa- 

 minations by Hoyer, Ma.x Schulize, and Lockhart Clarke 

 confirmed these statements ; and those of Schultze demonstrated 

 that the cells are of two kinds, one elongated and filled with 

 yellowish granular protoplasm, exposed at the outer end of each 

 cell and containing a clear oval nucleus in clear protoplasm in its 

 deeper part, which is first attenuated and then expanded into a 

 broad llaitened process, apparently connected with the connective 

 tissue ; the other cell, ilie proper ollactory cell, a thin, hbrous, 

 rod-like body, is monililorm or varicose, connected below with 

 the out-runners of a nerve-cell, and in birds and amphibia lur- 

 nished with one or more hair-like processes, which at the free 

 end come directly into contact with odorous particles. Exner in 

 1S72 denied the uistinctness of these two forms of cells, stating 

 that there are all intermediate forms, and that both forms aie 

 connected \\'\\\\ a deep network continuous with filaments of the 

 olfactory nerve. But Dr. Newell Martin, in a paper published in 

 the November number ot the JotiriuH oj Aimtomy aiiJ I'hysiology, 

 maintains that the two kinds of cell are aistnict, though their 

 characters approximate very closely in the instance of the frog. 

 He inclines to the belief that, as both lorms of cell are so distinct 

 from ordinary epithelium, they are all ollactory cells. 



The only conclusion which can be drawn from these obser- 

 vations is, that in this situation the ollactory nerves divide into 

 myriads of small finger-like processes, which, exposed on the 

 free surlace of the membrane, are actually engaged 111 feeling at 

 the odorous particles to inform us of their characters. 



This single instance, so thoroughly proved, would be sufiicient 

 to destroy our lormer ideas that nerves are spread out under base- 

 ment membranes and ne\'er penetrate an epithelial layer, 



But this is not the only case of tlii kind. Tne general rela- 

 tions of the gustatory nerves to the epithelial cells 01 the tongue 

 have been described by Axel Key as similar in the fuiigitorm 



