808 
ANATOMY AND PATHOLOGY 
strength to permit the introduction of the light- 
conducting system. Secondly, it is thin enough 
for transillumination and visualization of sev- 
eral muscle layers. 
The technique which we employed has been 
described in numerous publications. '^"^ To sum- 
marize briefly, cats anesthetized with sodium 
pentobarbital were used. Direct observation of 
the coronary microcirculation was accomplished 
through transillumination of the left atrial mus- 
cle. A hollow glass tube was introduced into the 
left atrial appendage. This glass tube had a flat 
upper surface which could be gently directed 
against the atrial muscle (Figure 1). Through 
this hollow light pipe, a round quartz rod was 
introduced. This was slightly smaller than the 
hollow tube and had a reflecting surface at its 
intracardiac end which directed the light per- 
pendicular to the axis of the rod and through 
the atrial muscle toward the objective of the 
microscope. This resulted in transillumination 
of a specific area of the left atrial muscle. The 
light source was a pulsating xenon arc. We 
made use of an intravital microscope developed 
by Wayland." This permitted the entire prepara- 
tion to be moved as a unit with respect to the 
optical train. In our more recent experiments, 
microcinematographs were taken on 16 mm 
color film at a speed of 400 frames per second 
with a Milliken camera. The linear optical mag- 
nification on the film was X30. 
The difficulties inherent in visualizing an ob- 
ject which moves in and out of focus are ob- 
vious. Efforts are therefore under way to design 
a servomechanism which will permit the auto- 
matic synchronization of the movement of the 
microscopic objective with that of the heart 
muscle. This is a joint project of the Jet Propul- 
sion Laboratory, the California Institute of 
Technology, and our institute. However, even 
though we have to deal with a continuously 
moving objective, we obtain several clear frames 
during both phases of the cardiac cycle by focus- 
ing on diff"erent layers. 
MICROSCOPE 
HEART IN SITU 
UNDER NORMAL 
CIRCULATION 
APPENDAGE OF 
LEFT ATRIUM 
(SCREEN FOR 
{ PHOTOS 
MOTION PICTURES 
WIDEO 
QUARTZ ROD 
(LIGHT PIPE) 
PURSE-STRING SUTURE 
Figure 1. 
