
Nov. 17, 1870] 
NATURE 
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THE MICROSCOPE 
HE VALUE OF NITRATE OF SILVER AS A REAGENT FOR DE- 
MONSTRATING MINUTE STRUCTURE.—Since Von Reck- 
linghausen drew attention to the beautiful results to be 
obtained by the use of a weak solution of nitrate of silver, 
in the study of the finer distribution of vessels, and 
especially of the lymphatics, much discussion has taken 
place as to the trustworthiness of results obtained by this 
method, and there are some histologists of merit who maintain 
that the whole thing is false and delusive in its effect. The 
method consists in immersing perfectly fresh (warm from 
the animal) tissues in a } per cent. aqueous solution of nitrate of 
silver, leaving them there for from five to ten minutes, and then, 
after thorough washing, mounting in glycerine, and exposing to 
sunlight for half an hour, or two or three hours as the case may 
be. If desired, the tissue may be plunged while fresh into serum 
(preserved with just a trace of iodine), and after two hours’ 
maceration therein may be smoothed with a small paint-brush, 
to remoye superficial epithelium (as, for instance, in the centrum 
tendineum of the guinea-pig), and then placed in the silver solu- 
tion. It is, however, preferred by Dr. Klein, of Vienna, to 
brush away the superficial epithelium of the thoracic surface, if 
the lymphatics of the centrum tendineum are to be examined, 
before removing the diaphragm from the body, whilst perfectly 
_ fresh and warm, warm water being used for this purpose, and a 
_ camel’s-hair paint-brush : immediately after this ‘‘pencilling” the 
centrum tendineum is cut out and placed in the nitrate of silver 
- solution. In the same way, in researches on the cornea the 
conjunctival epithelium may be remoyed in the living animal 
and the silver solution then applied. Dr. Klein, Professor 
Stricker’s assistant, has found that the best results were 
to be obtained with the cornea, by removing the conjunc- 
tival epithelium, and rubbing the corneal surface well with 
lunar caustic, and removing the cornea in half an hour's 
time. This method proves admirable with frogs, and is 
probably applicable to other cornez. The results of the 
nitrate-of-silver-staining as seen in the centrum tendineum, are 
that both thoracic and peritoneal epithelium (where not pencilled 
away) are stained, the outlines of the cells being brought out very 
distinctly. In addition to this the epithelium lining the vessels 
which run in the centrum is also brought out, and especially the 
curiously crenated epithelium of the fine lymphatics is demon- 
- strated. Moreover, Recklinghausen pointed out that small 
branched cavities become delineated connected by their branches 
to oneanother, and opening into the lymphatics with the crenate 
epithelium. These lacunar channels, ‘‘the juice canals,” are 
brought into view by the action of the silver in staining the sub- 
stance of their walls but leaving the cavity free. A szccessful silver 
preparation of the centrum tendineum of a guinea-pig, for in- 
stance, shows these structures clearly, but it is not always 
possible to succeed. Besides the remarkable epithelium of the 
_ lymphatics and the juice-canals, a hexagonal pavement of enor- 
mous cells is demonstrated on the nerve sheaths, and an ex- 
 ceedingly fine cell pavement on the adventitia of the small veins 
in some beautiful silver preparations of the ‘‘ centrum ” made by 
Dr. Burdon Sanderson. The results in the cornea are very 
remarkable, for the whole substance of that tissue in the frog is 
demonstrated to be filled with oblong radiating cavities, com- 
municating with one another by their branches, and of so angular 
and regular a character as to give the appearance of a mosaic- 
work or some such elaborate device. These cavities correspond 
to the juice-canals in the centrum tendineum, it is by their means 
_ that the cornea is nourished, it is they which contain the large 
star-like cells or protoplasm-masses brought out by gold chloride, 
and it is along their branches that the divided portions of these 
cells wander so remarkably in the process of inflammation. And 
now we are told by some persons that these are artificial pro- 
ductions, that the juice-canals and the radiate lacunee, and the 
crenate lymphatic epithelium too, are due to fortuitous coagula- 
tion caused by the silver, that they do not represent structures 
existing in life. There are two sets of objectionists, some who 
deny the whole thing, others who go so far as to deny the 
juice-canals and stellate lacunze, but admit the epithelium. An 
exponent of the first order is a certain Dr. Robinski, who in a 
paper published in the excellent Archives de Physiologie of Brown- 
_ Séquard, pretends that the crenate epithelium which so many 
have seen in the finer lymph vessels, as well as the juice- 
canals, are due to imperfect retention of portions of the 
superficial epithelium, and gives a drawing intended to show 





this. The author of the paper has simply failed utterly and 
entirely in using the method, and the outrageous view 
which he advances does not require refutation. Everyone 
knows who has made silver preparations successfully that 
the thoracic, the lymph-canal, and the peritoneal epithelium 
may all be seen lying one over the other in parts of a preparation, 
and that the form of the second prevents its being mistaken for 
the first or third. Others maintain that the crenate lymph-epithe- 
lium is simply a form due to the silver, and not to cells at all. 
This is impossible, because the nucleus and cell-contents are 
sometimes clearly demonstrated, and moreover the same form of 
epithelium may be readily obtained from large lymph-sacs, of 
some of which it is characteristic. The juice-canals, if they 
appear doubtful at all when taken by themselves (which indeed 
they do not if a good preparation is examined), when seen in the 
light of the stellate lacunz of the frog’s cornea, are clearly under- 
stood, and must be fully admitted as normal living structures. 
There are, however, persons who object to these, among whom 
is so eminent a histologist as Professor Schweigger-Seidel, and 
also that accomplished micrographer, Dr. Ranvier, of Paris. 
They actually hold that these forms are ost-mortem products, 
the effect of the action of nitrate of silver on the albumen and 
gelatine of the tissue. It is almost as strong a position to take 
up as that of certain schoolmen who maintained that we know 
nothing of the anatomy of living animals, since the air admitted 
on cutting them open, and the scissors, produced all the va- 
rious viscera seen in a dissection. There are some strong 
facts which we have witnessed which render such a view un- 
tenable. In the first place, the stellate lacunze of the frog’s 
cornea are shown in a preparation in our possession, with 
the intermediate substance stained by go/d and the lacune 
and cells unstained, in fact, exactly the same appearance as 
is produced with silver. Hence the stellate form of the lacunze 
cannot be due to a specific action of the silver. Again, by 
silvering the living comea whilst it is still part of the frog, 
the structure is brought out, and may be obtained of all de- 
grees of intensity, the /ovm, however, always remaining the same, 
and not varying with the amount of silver allowed to act on it, 
as might be expected had we to do with a precipitation-form, 
which should appear less completely developed when less silver is 
used. Moreover, the living cells were thus demonstrated lying 
in these stellate lacunze, creeping up the radiating branches, 
drawing back again, and creeping along others, thus obtaining 
that curious direction to their movements which one always ob- 
serves in studying them in the fresh, unstained, inflamed cornea. 
The necessity of admitting that the normal structure of the frog’s 
cornea is brought out by the silver method, covers also the 
question as to the similar structures in the centrum tendineum, 
The ‘‘ Saft-canilchen ” must equally be admitted as having a 
living existence, and are not due to the imaginary precipitating 
action of nitrate of silver on some albuminoid, as Schweigger- 
Seidel would have us believe, but a parallel to which he cannot 
find. The chief difficulty with regard to the crenate epithelium 
of the lymph vessels in the centrum tendineum is to explain why 
we only see one layer of these cells; they should appear all 
round the wall of the vessel so as to produce a double layer 
as we look through it, but we only see one layer, the other not 
being stained. ‘The action of light, the absorption of the silver, 
and other causes, may be hazarded as explanations of this ; but 
it would be satisfactory to get a double layer clearly shown. 
So far, then, from agreeing with Schweigger-Seidel and other 
objectors, that the silver method of Von Recklinghausen ‘ gives 
no true indication of the structure of the cornea,” nor of similar 
structures, and ‘‘should be abandoned,”* we believe that when 
carefully applied it furnishes most admirable results, difficult to 
attain in any other way at present in our hands, and is worthy of 
all confidence, and should be used as a means of investigation in 
other structures besides those to which it has been already ap- 
plied. EB, R.L. 

REPORT OF THE KEW COMMITTEE OF THE 
BRITISH ASSOCIATION FOR THE ADVANCE: 
MENT OF SCIENCE FOR 1869-70 
“THE Committee of the Kew Observatory submit to the 
Council of the British Association the following statement 
of their proceedings during the past year :— ; 
At the meeting of the General Committee at Exeter it was re- 
* Berichte der Math, Phys, Classe der Kon. Sachs. Gesellsch, 1869. p. 352. 
