May 7, 1908J 



NA TURE 



19 



that of Fig. 2, which shows a section of cow-hide tanned 

 with oak bark and curried with d^gras. 



Before describing Fig. 2. it is necessary to explain the 

 mode of preparation of the section. A small strip of 

 leather about 10 mm. wide is taken 

 shaved away until the piece has a 



and the flesh side 

 thickness of about 



2 mm. The shaved strip is placed in melted tallow, not 

 too hot, for about a quarter of an hour ; after cooling, the 

 strip is embedded in hard paraffin and cut in a Ranvier 

 microtome, the sections degreased with xylol, then washed 

 two or three times with alcohol, and stained with Weigert's 

 fuchsin ; the staining takes about three hours ; the 



Weigert solution is poured off, and a few drops of abso- 

 lute alcohol put on to the section ; this removes excess of 

 dye, and differentiates the various parts. It is now 

 washed twice with alcohol, passed two or three times 

 through xylol to eliminate the alcohol, and finally mounted 

 in balsam. 



NO. 2010, VOL. 78J 



In M. Boulanger's view, the skin, when freed from the 

 hair and the histological epidermis (both of which are got 

 rid of in the preparatory processes), is composed of two 

 tissues, an upper and a lower, intimately united, although 

 of distinctly different natures. No scientific designation 

 has been given to these two distinct layers, but the whole 

 has been called the dermis ; in view of their special con- 

 stitution, and to distinguish them, he calls the "grain" 

 the fibro-elastic layer and the " flesh " the layer of giant 

 connective fibres. The elastic fibres in their natural state 

 take up Weigert's stain readily, and they retain this 

 property after tanning ; both before and after the tannage 

 they form the essential framework of the skin or leather; 

 without them there is no elasticity or suppleness, and 

 tanning does not appear to alter their constitution. The 

 connective fibres, on the contrary, are completely changed, 

 ^o that we may conclude that the tannin acts differently 

 on the two tissues. 



The present writer will not here discuss this conclusion, 

 though in his opinion there is no such distinct difference 

 between the two portions of the skin, but that in the 

 " grain " the connective tissue is fine and closely com- 

 pacted, whereas in the " flesh " it becomes loose and 

 coarse ; thus the difference is in degree, and not in con- 

 stitution. Boulanger's iibro-elastic layer must not be con- 

 founded with the elastic vellow fibres which form a 

 comparatively small part of the volume of the skin. Com- 

 paring the two figures, there is a striking contrast in the 

 general setting of the elastic fibres. In the raw skin 

 they ramify in all directions, whereas in the tanned skin 

 they onlv exist in a longitudinal direction, as a conse- 

 quence of the dilation and preparation that the skin has 

 undergone. 



M. Boulanger has utilised his method in the study of 

 leather for use as belts, &c., the results of which are 

 published in his book, " Essais du Cuir dans ses Applica- 

 tions industrielles." There is no doubt that the method 

 of microscopic examination of leather might be of con- 

 siderable use after much practice in the manipulation and 

 comparison of various leathers has been acquired. It 

 would then be possible to determine whether the leather 

 under examination had been made from a salted skin or 

 a fresh skin, of European origin, or from a foreign dried 

 skin, the sex of the animal, cow, ox, or bull ; whether 

 the leather had been adulterated, overloaded with tannin 

 or weighting materials, &c., in short, the history of the 

 pelt might be deduced from the study of the tanned leather. 

 Let us hope that the younger generation of tanning 

 students now being trained in the leather industries depart- 

 ment at the University of Leeds and at Herold's Institute 

 in Bermondsey will keep up the reputation of Eneland in 

 this work. " J. T. W. 



THE ATOMIC WEIGHT OF RADIUM.' 



A LTHOUGH there has been a considerable amount of 

 "^ discussion, based upon spectroscopic considerations 

 and on its supposed mode of genesis, respecting the place 

 of radium in the system of the elements, and inferentially, 

 therefore, concerning its atomic weight, we are indebted 

 for the only direct experimental determinations of this 

 value hitherto made known to the discoverer of the element, 

 Mme. Curie. Her first observations, published in 1902, 

 were made on about 90 milligrams of the chloride, and 

 furnished the value 225. 



In the autumn of last year Mme. Curie communicated 

 to the French Academy the results of a second series of 

 estimations made upon' about 4 decigrams of the carefully 

 purified chloride ; these afforded the value 226-2 as the 

 mean of three closely concordant determinations (Ag= 107-8, 



Cl = 3S-4)- 



In igo6, at the instance of Sir William Huggms, then 

 president of the Royal Society, and by the aid of the kind 

 interest shown bv H.R.H. the Prince of Wales, the 

 .Austrian Government placed about 500 kilograms of pitch- 

 blende residues from Joachimsthal at the disposal of the 

 Royal Society. These residues were worked up by M. 



1 Bakerian Lecture for 1907. Delivered at the Royal Society by Dr. T. E. 

 Thorpe, C.B., F.R.S. 



