104 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
return to our former simile) a picture of a hayrick instead of a dog, 
while he insists that a small cone is preferable to a large one lest the • 
dog appear foggy. To which I reply that a foggy dog is preferable to a 
hayrick, however sharp. 
When the illuminating cone is enlarged so that it fills about 3/4 of 
the back of the objective, one image, and one image only, can be 
produced, which, as I have said, goes in and out of focus as a daisy 
under a 4-in. There can be now no doubling of the structure, and 
no multiple images are produced. Spherical aberration in the lens 
merely veils the image under an appearance of fog or mist. The clear- 
ness and distinctness of the image may be marred by its means, but the 
image cannot be altered in form. 
1 have only one more point to bring to your kind notice, and that 
is the statement that the wide- angled cone, by means of the superposi- 
sion of dissimilar images, obliterates uncoloured histological tissues.* 
The truth regarding this is that the wide-angled cone gives you a 
faithful representation of uncoloured histological tissues (very likely 
not the preconceived images regarding them), blotting out all those 
parts which are out of focus. In other words, it gives you a truthful 
picture of a definite plane in the structure. To illustrate this I have 
selected the thinnest and most transparent histological object, and one 
which would be more likely to be blotted out than any other with which 
I am acquainted. I have photographed this both with a wide and narrow 
cone, and you shall judge for yourselves which is the more faithful 
picture. The object is cartilage in a young rat’s tail, of which I will 
project a low power view, X 8, in order that you may identify it. I 
now show you an image (fig. 17), X 390 diams., taken with a small 
cone. The most prominent features in this image are the parts which 
are out of focus. I wish to draw your particular attention to a cell- wall 
seen end-on running nearly in a vertical direction in the centre of the 
slide. The focus was adjusted precisely on that point, and I would like 
you to notice the apparent thickness of that line. 
I will now show you the same object (fig. 18) taken by a large cone, 
and you will at once understand the extreme tenuity of that particular 
cell- wall which in the previous picture was so thickened by false 
diffraction ghosts. This picture, I maintain, is a true representation of 
an exquisitely thin cell-wall ; there is no blotting out of any structure 
in focus, only a removal of false diffraction ghosts. Of course it may be 
useful to produce a false image for the purpose of obtaining an idea 
as to the relative position of the part in focus to those parts out of focus. 
But this has nothing to do with the bare fact of the obliteration of 
structure by means of a wide cone. 
In conclusion, I believe the objection to the use of a narrow-angled 
cone to be due to the fact that it emphasizes zonal differences, and the 
efficacy of the wide-angled cone that it as far as possible neutralizes the 
effect of those differences. Prof. Abbe states (p. 724) “ there is not the 
least rational ground, nor any experimental proof, for the expectation 
that this mixture [he is alluding to the mixture of slightly dissimilar 
images in consequence of the employment of a wide cone] should come 
nearer to a strictly correct projection of the object than that image which 
* R.M.S.J., 1889, Part G, p. 723. 
