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210 I Transactions of SM.P.E., February 1927
of an acetylene flame or even a kerosene flame for fine detail with high power lenses and turned the broad side of the flame for lower powers with less fineness of detail.
The small pencil arcs with from 4 to 6 amperes capacity on direct current closely approximate the ideal as regards a point source of light and the heat which they generate may be largely absorbed by a water cell. However, with higher magnifications, more and more light is required with the resulting heat so great as to present a serious problem, not alone for injury to the organism under observation, but for the delicate lenses of the instrument as well.
Water cells are useful but inadequate for the higher amperage arcs and the problem of heat elimination at high magnifications still remains a very serious problem. Comandon curtails his light by means of a synchronized shutter mounted between the light and the microscope. This shutter is directly connected with his motor drive mechanism and is in turn connected with the camera by means of small shafting and universal joints. Thus his light reaches the microscope in a series of flashes so that the prolonged heating effect of concentrated light is avoided.
In the case of this French worker, such a refinement is doubtless justified since he has, no doubt, secured photographs of far greater magnification of living organisms than have ever been attempted by other workers. His work has dealt with living organisms such as those which produce syphilis and sleeping sickness and I have even been shown, by him, a film which records the complicated changes of the chromosomes within a dividing white blood cell. But all such work is so advanced and specialized as to be unique. Personally, in all my experience, I have never been called upon but once to equal such a magnification. For the lower powers of 50 to 200 diameters the problem of heat is not as serious as is generally supposed. A cold light would be advantageous — often I have killed my organisms from heat — more often they have refused to perform properly under such conditions of heat and light but only once have I melted the balsam of a lens or in any other way injured my apparatus by heat.
In my experience I have used many sources of light. A clock work arc by E. Leitz was my first lamp and much of my best work was done with it. However, it was always a source of annoyance to me since it would rarely remain in adjustment for more than 7 minutes. I worked without assistance and this light had a way of going out at critical moments which tried my patience to the limit.