The Capillary Microscope:

Viewing human blood cells & circulation in vivo.

by Peter Abrahams, Portland, Oregon, USA



Zeiss offered a microscope for this purpose in 1930, the "Zeiss finger capillaries examining microscope". The illuminator used aspheric lenses, and the 5 amp arc lamp required a special fluid cell for cooling. The objective is described: "M 8n. A. 0.20".

Leitz microscope catalog V-A (after 1929), offered two models of finger capillary microscopes. Page 91, Small Skin (Capillary) Microscope SC, a simple drum type microscope. Pages 92-3, Large model LC. These included a special photographic objective and 'contrast' filter (green to cut the diffuse red glow?). They could be placed on other areas of skin as well, which was covered with cedar oil to aid transparency.

This catalog includes photos taken with these microscopes, of what looks like several dozen narrow, twisted, dark arches in a foggy matrix. Visual magnification would be about 60 power, and small features are not sharply imaged. The Zeiss microscope is for viewing the 'limbus' (edge) of the nail. The Leitz is for viewing the 'nail-fold' of the index finger. Both manufacturers supplied powerful illuminators, set up as oblique, overhead light sources, with heat filters.

There is a modern video capillary microscope, see: which includes a Laser Doppler Anemometer for measuring blood cell velocity in single capillaries in real time.

Extract from Lewis, Thomas. Exercises in human physiology (preparatory to clinical work). London: Macmillan, 1945. 103p. p39. (See safety notice below.)

Capillary Microscope. To view the human capillaries requires the right apparatus and some patience. The best apparatus is a binocular dissecting microscope, moving freely in a horizontal arc, and having a coarse and fine vertical adjustment; but much can be seen on the stage of an ordinary microscope. The magnification should be from 10 diameters to 50, according to the amount of detail required. An essential adjunct is a strong beam of light, filtered through a dark blue or green screen; and a beam that can be focussed on any desired point; the red rays of the concentrated light would burn the skin, a green or blue light helps to bring the vessels into view.

The most convenient place to view the vessels is in the skin at the base of the middle or ring finger nail. The horny layer of skin should be allowed to grow forward over the nail for a week or longer, for this brings the loops more at right angles to the line of vision. Decide upon the stand on which the finger is to be placed for examination, the arm and hand being in a quite unstrained position, and arrange a bed of Plasticene® that will gently but securely hold the finger. It is possible but not so easy to examine one's own finger. With a razor blade shave away skin at the base of the nail, cutting parallel to the surface and taking off most of the horny layer without drawing blood. Fix the finger on its stand and place a drop of cedar wood oil or liquid paraffin on the surface to be examined. The microscope should be brought to bear almost at right angles, and the beam of light at about 45 degrees. The first essential is to obtain a view free of light reflex, and this the oil greatly helps. The capillary loops at the base of the nail will be brought to view readily by this means under a low power, and high power may be substituted. Do not be disappointed if the outlines of the capillaries at first seem misty; it is surprising how much improvement of view minor adjustments, better lighting, and especially very close observing will bring.

Congestion and its effects. Having obtained a view of the capillary loops, and these with a few of the minute venules into which they lead is as much as is usually visible; impede the return of bloodflow through the arm by congesting the veins. As soon as the skin becomes engorged the capillaries and venules will swell and become more prominent. Morever, because the obstruction slows the flow of blood in the vessels, this flow will become much more distinct. When really slow, the individual blood cells can often be seen as they pass, white cells being recognisable from red by their higher refraction. The stream of blood is most difficult to see when it is very rapid, the corpuscles become blurred, as do the spokes of a rapidly revolving wheel. See the flow when it is slowed down, and the flow can be increased at will until it is full again.

Arterial occlusion and its effects. Stop the flow to the arm and note how long it takes for the blood to come to a first standstill in the capillaries; often it ebbs and flows before coming finally to rest.

Blistered skin. Much clearer views of the vessels can be obtained if the horny layers of the skin are first removed by a blister, though this brings the vessels into a state of full inflammatory vasodilatation, and a little surface coagulum must be wiped away from some time to time. In some such preparations the vessels stand out as clearly as those in the frog's web.

A very clear view can be obtained of the flow in the vessels of the sclerotic; in this case, however, it is necessary that the subject should be able to fix his eyes very steadily on one object for appreciable periods.

American Journal of Physiology, v29, p335.

Heart v11, p171. Thomas Lewis. Univ. College Hospital, London.

Comments to the author Peter Abrahams are welcomed.

The author's web site on the history of binoculars & telescopes is at


Micscape Safety note: the procedures described in the book extract above are for interest only and Micscape is not suggesting these are carried out. OnView Ltd, Microscopy UK, Micscape and its contributors accept no responsibility for harm to persons or property if this guidance is not adhered to.



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