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The lucite calvarium for direct observation of the brain in monkeys. Modified methods for installing large and small removable windows by indirect fixation

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THE LUCITE CA4LVARIUM FOR DIRECT OBSERVATION OF THE BRAIN I N MONKEYS
MODIFIED METHODS FOR INSTALLING LARGE AND SMALL REMOVABLE
WINDOWS BY INDIRECT FIXATION
DAVID MINARD,’ ELLIOTT F. OSSERMAN AND S. ROBERT HOWELL ’
Naval Medical Research Institute, National 3‘aval
Medical Center, Bethesda, Maryland
SIXTEEN FIGCRES
INTRODUCTION
A method for replacing large areas of the bony calvarium
in monkeys with a molded lucite plate designed to restore
a rigid cranial enclosure while permitting visualization of
both cerebral convexities has been described by Shelden et
al. (’44). These authors term their preparation “the lucite
calvarium” to distinguish it from the small flat cranial windows previously employed by other investigators (Forbes,
’28; Wentsler, ’36; Sohler, Lothrop and Forbes, ’41). Forbes
(’28) and Shelden et al. (’44) have reviewed the earlier
literature on this subject.
The lucite calvarium when attached directly to the skull
must fit with a degree of accuracy sufficient to prevent leakage
of cerebral spinal fluid (CSF). The present paper will describe a modified method for preparing the lucite calvarium
designed to improve control of CSF leakage through indirect
fixation of the plate to an implanted ring. This modification
also facilitates removal and replacement of the window for
later procedures.
‘LCDR (MC) USN.
* Lt. (jg) (MC) USNR. Piesent address : Fraiicis Delaficld Hospital, New
York, N. Y.
3CDR (DC) USN. Present address: U. S. Naval Mineeraft Base, Charleston,
s. C.
317
318
1). JIISARD,
E. F. OSSERMAX A N D S. R. HOWELL
METHODS O F PREPARATION AND OBSERVATION
T h e lucite cnlvariunz
The original method of Shelden et al. requires two stages
of operation: The first consists in exposure of the skull, removal of bone from the window areas, and taking an impression. From this impression a model is made in dental stone
upon which a wax pattern is molded f o r fabricating the lucite
plate. I n the second operation, the dura is resected and the
lucite calvarium attached directly to the skull.
The implanted ring modification to be described differs
in that the lucite window is attached to a closely fitting metal
or lucite ring implanted on the skull several weeks prior to
removal of the bone. This allows time for tissue regeneration
to fill any remaining gaps between the ring and skull.
First stage operatiom. The skull of the anesthetized monkey is exposed through a Y-incision. The periosteum is
removed and the origins of the temporal muscles resected.
An impression of the skull is taken using a contoured tray
filled with dental hydrocolloid.
Fabricathn of the ring. From the impression a model of
the skull in dental stone is prepared. This is duplicated in
investment plaster and on the latter model the pattern of the
ring is fashioned in wax. Details of making the mold from
the wax pattern are given in one of the above reports (Minard
and Howell, '49).
The exposed surface of the early rings were smooth or
designed with a narrow shelf upon which the overlapping
edge of the lucite plate rested. The later designs provide a
groove f o r seating the edge of the plate and into which sealing
compound can be firmly packed. The rings have 4 screw
holes along the lower border for attaching the ring to the
skull. Six stainless steel nuts (2-56) are embedded in the
upper border for bolting the plate to the ring. Ticonium, the
metal used for casting the ring, is a chrome-cobalt-nickel
alloy which melts at temperatures between 2300°F. and
T H E LUCITE CALVARIUM IN MONKEYS
319
2400°F. Its hardness makes drilling and tapping impossible.
I n a final preparation (monkey no. 11) a lucite ring was
employed. Embedded nuts were not used. Instead the plate
was welded directly to the ring with a rapidly setting methacrylate resin.4
8econ.d stage operatiom. Approximately one week after
the initial operation the skull of the anesthetized monkey is
again exposed and the completed sterilized ring attached to
the skull with 4 vitallium finger plate screws 5 mm in length
(fig. 1).
T h i r d stage operation.. After an interval of at least 4
weeks the skull and ring are again exposed using care to
avoid dislodging the new tissue which has formed between
the two. It is upon this new tissue that the fluid tight
contact depends. Bone is removed from the window areas
(fig. 2). The dura is left intact. A second impression is now
taken which must include the ring.
Fabrication. of t h e lucite plate. From this impression a
model is prepared in dental stone, upon which a wax pattern
of the plate is fashioned. From this a mold is made and the
lucite plate molded under heat and pressure as described in
greater detail in the original report.
Fourth stage operation.. About one week after the third
operation, the ring and dura are again exposed. Holes are
drilled in the lucite plate in alignment with the 6 nuts embedded in the ring. The dura is resected applying electrocoagulation to bleeding points. The plate is then reseated on
the ring (fig. 3 ) and bolted into place with 6 stainless steel
bolts (2-56).
The groove is carefully packed with bone-wax or guttapercha, and the heads of the bolts and the groove are coated
with a rapidly hardening cement. The final step is the resection of the scalp. The animal is placed in a recovery cage
with a dry dressing held in place by a closely fitting cap.
‘
Nu-Weld,’ ’ a preparation available through dental supply houses,
Registered trade name. Austenal Laboratories, New York, N. Y.
320
D. MINARD, E. I?.
OSSERMAN AND S. R. HOWELL
Penicillin is started on the day of final operation and continued f o r about a week.
ONe-inch wiwi?ow preparation
The principle of indirect fixation of lucite windows t o an
implanted ring has been applied to a smaller window which
can be installed in monkeys in a single operation through
the use of a prefabricated vitallium ring6 into which the
flat disc-shaped lucite window is threaded (Osserman and
Minard, '52).
The essential components of the vitallium ring and window
assembly are illustrated in figure 5. The circular ring is
cast in one piece and consists of a shallow lip which slips
into the skull opening, a shoulder which rests on the margins
of the opening, the external portion which projects above
the skull and is threaded inside to accept the threaded lucite
window and outside for the protecting cap, and 6 perforated
flanges, three anterior and three posterior, f o r attaching the
ring to the skull with vitallium screws. The lip and shoulder
are contoured to fit a cylindrical surface of 5-inch radius
which approximates the transverse curvature of the monkey
skull in the parietal region. The flanges of the ring conform
to the flatter anteroposterior curvature.
I n the operative procedure the skull is exposed through
a circular scalp incision about one inch in diameter. The
head is fixed at three points in a special holder (fig. 6)7
which holds the head and cutter in rigid relationship. The
cutter having been positioned, all adjustments are tightened
leaving the hand operated tool free only to rotate and to
move back and forth in a direction perpendicular to the bone
surface.
After cutting through both bony tables of the skull, the
operator removes the button of bone, resects the dura, and
Manufactured by Austenal Laboratories who contributed valuable advice in
the design of the ring.
Designed by Dr. Gcorg Madelung of the Naval Medical Research Institute.
@
THE LUCITE CALVARIUM IN MONKEYS
321
fixes the vitallium ring in place. Two windows can be installed in the same or separate operations.
A simplified form of cutting instrument has been designed
by workers at the Naval Air Development Center, Johnsville,
Pa. (Duane et al., '52), which consists of concentric sliding
cylinders., The outer one serves as the guide, and is attached
by screws to the skull, while the inner cylinder carries the
cutting tool. The instrument has been used successfully in
the installation of the one inch window in 16 monkeys for
studies of brain circulation during headward acceleration.
METHODS O F OBSERVATION
The following special techniques have been employed f o r
viewing the pial vessels :
Slit lamp illumination. The slit lamp together with the
binocular dissecting microscope enables the observer to detect early abnormalities in the CSF. Cells suggest beginning
infection and prompt treatment is indicated. Further, the
slit lamp defines the depth of the fluid space.
Surface reflecting micmscope.8 This instrument has proved
of special value in the examination of the small windows.
Special thin windows have been installed to permit closer
working distance s.
I n contrast to the large molded plates, the small windows
can be made optically flat and are potentially useful at higher
magnifications.
Ultraviolet iZZunzination. Sodium fluorescein which is a
non-toxic fluorescent dye of the acid group fails to stain
brain (Friedemann, '42). Following its injection, however,
the initial appearance and the passage of this dye through
the exposed pial vessels illuminated with long wave ultraviolet light can readily be studied either by eye, camera, or
photofluorometer. By using an automatic syringe for dye
injection (Xinard and Osserman, '50) and cin6photographic
or photofluorometric methods f o r recording, it is possible t o
' Leitz Ultrapak.
322
D. MINARD, E. F. OSSERMAX A N D
s.
R. HOWELL
time these events objectively and to obtain a record for later
study (Minard, ’50; Minard, Osserman and Eicher, ’50). The
photographs shown in figures 13, 14, 15 and 16 are enlarged
from a single 35mm cine film record taken with a camera
operated at 4.8 frames per second. Phases in the passage of
the dye are illustrated. This method of viewing clearly differentiates the successive segments of blood vessels, and
reveals these vessels in sharper detail than by ordinary
illumination. Since regenerating vascularized fibrous tissue
retains the dye, fluorescein injection provides a means of
studying the rate and extent of tissue regeneration.
RESULTS
Lzicite caluarium. Five cats and 1 2 rhesus monkeys were
used in these studies. Nine of the 12 monkeys are listed in
table 1 together with essential facts including the period of
time during which the vessels remained clearly visible (“useful period”) and the presence and extent of CSF leakage.
Three monkeys not listed are: no. 8 which died three hours
after the final operation; no. 10 in which the operative wound
broke down following the second operation; and no. 12, an
animals in which the preparation was not completed.
The use of the ticonium ring without the groove led to
improved leakage control as compared with direct fixation
but intermittent leakage still occurred. Removal and replacement of the plate t o treat local sites of infection was carried
out with ease in this group, a procedure which usually resulted in temporary restoration of vessel visibility.
The grooved ring represents a distinct step forward in
the control of leakage. I n the case of monkey no. 6 no leakage
was apparent for over 7 months, during most of which time
the fluid remained clear. At about 8 months the lucite plate
was removed, cultures taken, the membranes lavaged, and a
window made in the regenerated membrane. The lucite plate
was replaced and sealed. The fluid remained clear and the
exposed pial vessels distinctly visible for another two months.
Ten months after the original preparation bilateral clouding
'Key:
kg
3.7
hf
9
11
17
3.6
4.2
4.9
M
F
F
3.6
3.2
4.9
3.8
3.2
6
~~~~~~
M
M
F
F
F
SFX
5
4
7
I
1
3
MONKEY
(c)
(b)
(a)
DATE
0
14
days
USEFUL
PSRIOD
61
Metal ring with groove
10-13-47
78
2- 4-48
41
7-14-48
35
Metal ring without groove
3-10-47
19
6- 9-47
22
8-1 3-47
28
12-18-46
3-31-47
COMPLETED
Lucite ring
4
9-29-48
4
4
4
3
4
4
0
2
NUMBER O F
STALQEBIN
P&EPA&ATION
Results of preparations in nine monkeys
'
0
+
+
+
++
++
C8F
LEAKAGE
Gross leakage incapable of being controlled.
Gross leakage intermittently; capable of bcing controlled with difficulty.
& Minor leaks occasionally observed; readily controlled during useful period.
0 No leakage observed during useful period.
+
++
Indirect fixation
Direct fixation of
plate to skull
TYPE OF
P R ~ A ~ * ~ O N
TABLE 1
Ludte calvarivni
RzzEA:t
&,
0
1
1
0
4
3
2
0
0
EEPLACEMEXTS
OF CALVARIUY
Not hkeu
Staph. aureus
Staph. aureus
Not taken
Not taken
Staph. aureus
Proteus morgani
Not taken
Not taken
BACTERIOI.OUICAL
CULTUlbE FRQH
BRAIN SURPACE
H
B
324
D. MIXARD, E. F. OSSERMAN A N D S. R. HOWELL
occurred in spite of antibiotic therapy and no further attempt
was made to restore visibility.
Monkey no. 11 was prepared with a lucite ring to which
the plate was permanently cemented. For two months no
CSF leakage was evident and there was no sign of infection.
However intermittent oozing of blood occurred from small
vessels growing into unfilled crevices between the ring and
plate. This usually cleared completely in a day or two. The
useful period was terminated at 61 days by evidence of infection with rapid clouding of the fluid which failed to respond
to therapy.
One-inch window preparution. The small window was inserted on one or both sides of the skull of 5 monkeys. Leakage
has not been a problem. Infection which occasionally supervenes within the first few weelis, can usually be controlled
by intramuscular antibiotics alone or in conjunction with
local irrigation and topical application of powdered antibiotics.
DISCUSSION
I n the absence of infection the useful period of the cranial
window preparation is limited only by the gradual ingrowth
of fibrous tissue. This process has been described in detail
by earlier investigators using small permanent windows in
surviving animals (Wentsler, '36 ; Sohler, Lothrop and Forbes,
'41). I n the present preparations this is easily corrected by
detaching the window, excising the new membrane and replacing the window.
Unfortunately in most preparations infection sooner or
later takes place. Whether bacterial contamination of the
exposed pia-arachnoid occurs during the final operation or
later after the plate has been attached is not definitely established. It is known however that signs of infection appear
earlier in animals exhibiting gross CSF leakage than in
preparations with little or no apparent escape of fluid, This
suggests that the infectious agent enters the chamber during
the post operative period by the same channels as those
THE LlJCITE CATAVARITJM 1N MONIIEYS
325
thiwugh which spin.al fluid escapes. It would seem axiomatic
tlicrdoie that t,o corit,rol infc<:t,ion one must first control
Icakage.
I n our hands t.hc grooved rrictal ring for attaching large
molded windows and the one-inch vita;llinm ring for holding
flat threaded cranial windows arc useful procedures wliich
cornhinc good control of CRF leakage with case in removing
and repla.cing the plate. The lwite ring also gives excellent
leakage c.ontro1 hut the p1at.c is pernimently at.t.ached.
There have been at.t.emptsby others to modify the original
procedure of Shelden ct al. Thus, onc group (Spit.z, '4i) '
obtained good results in a two-stage procedure by a.pplying
it rapidly sct.ting dendal cement l.O to the c.ont.act edge of the
pla.te just. prior to wiring or bolting it to the skull of cebus
monkeys. Recently IIuertas ( '54) l 1 has devised a one-st.ep
operation which employs a plate previously molded from an
impression taken with t.he scalp intact,. He reports 5 successful preparations lasting up to two months. Brackett ('54) l 2
has uscd thct ring techriic~uewith success but plans to adapt
the same principle to a one-st,age pr*ocedure.
Tlie dcvclopment of an acceptable one-stagc? rricthod f o r
iiist'alliiig l u g e molded windows will doubtless be welconicd
by tliosc who no\v hesitate t,o use the lucitc ctzlvnrium in their
studies because of the time and effort required in the prepai*t?tioii. However even if a succcs;sful single-stage method is
devised, certain limitations will continue to restrict its use :
the necd for. sliilled assistance ; meticulous and time consuming
at.teiitioii in thc postopcrat,ive (:are ; opt,ical lirnitntions of l.hc
p1at.c; a.nd finally the lack of data on t,he physiological disturbanc.es caused by the preparation itself.
Tbc invest.iga.tor is caut.ioncd, therefore, to consider carefully the 1-equiremet1t.sof his st.udies before undcrt.aking the
large window preparat.ions. A suitable application is best
' Address:
TTniwrsity of Pennsylvania Mcdicinl Hehool.
Konfoi-mag, maiiufac.t.ured by K.onforinnx Laboratories, Tile., Rrooklp, N. P.
'' D c h i l s of prep:ir:ition o l h i n e d by personal eommunication.
l Y Present address: CnkersitF of
K:ins:is Medical Cent.er, Ti:insns Cit.?, Kansas.
I"
326
rj.
MISARI),
E. P.
ossIcKnr.ix
AXD
s.
R. HOWELL
illustrated by the one for which the prcparation was origir1aI1~-designed : an analysis by higli-speed photography of
braiu movements within the closed cranium when the head
is su1)jectc.d l o iiiipact ( h d c n z and Shelden, '4G). Another
w ~ l chosen
l
application is a current study of regional changes
in cwe1)ral hlootl flow rcsulting from experimental occlusion
of ccrcbral vessels (Ttraclcctt, ?54). I n general the lucite calvai-iuni is useful in visualizing a single large area of the brain
within a closed craiiial vault, or in comparing vascular conditions in smaller rcgions sitiiatCd within the window area.
\V'hcricvcr it smaller area will serve as a rcyresentativc
saiiil)le of the hrain surface as a wholcl, tlie oue-inch window
is tlic nic>lliodof choice. Thc preparation is i~ one-step procedurc utilizing prefabricated eleiuents, and postoperative
B ~ I I Y is rclu tirelp simple. Furthernioi-c\ the optical qualities
of the flat disc are superior to those of the molded plate.
'I'h onc-inc~h1~7iridowand vitwlliuni Iioltler described here
tliffrr only in detail from the cranial windows employed so
fiwitfully by Elorhcs tinti his i ociates. The present window
oflers a sonicwhat larger IYiew and can he quickly removed
:tiid i ~ p l a c e dundcr ascptic conditions without disturbing the
contact bctwccn the i i t ~ t a iring and bone margin. Thus the
risk of su1)sequcnt iiifcction anti lcakage is minimized.
R I - V ~ I A R Y.I N D
mmv~,rsross
I . A niodificbd 4-stiigc procedure for preparing the lucite
caIvai*iuni in r l i w u h rnonltrys is tiescribed in which a molded
~~7iiiclow
is bolted to a grooved ticoninm inctal ring or cemented
t o a lucitc ring p c v i o n d y implanted on the skull.
2. A one-stag(\ pi*ocedui*ef o r installing removable oneinc~liIucitc wiiidows it1 oiic or both parictal areas of inonlteys
by means of permanently attached prefabricated vit a11'iuni
rings is also dcsci*ibcd
3. S p e c i d niethods f o r observing thc hrain vessels are
outlined iit(a1udiiig thc iiw of the slit-lump, the surface reI11e;\siircni(:ilts.
flecting iiiiciwwoi)c, uiid fliiorescen~~
T E E LTJCITE C I L V A K I U X I S XONKEPS
327
LITERA.TURE ClTED
GRACKETT,
c‘. E., J K . 1.9’54 Personal comiiiniiicatioii.
Studies
1952
DUANE,T. I).,R. T.,. WE(:IISI,ER,J. E. ZIICGLIU~,
A N D E. I,. I ~ R C K M
~
o n cerelwal pliysiology of monkrys at 1.3 nrgat.ive C . J . Aviation Mcd.,
23: 4 7 9 4 8 9 .
FORBES,
IT. S . 1938 The c,erebr:il cireolntion. I. Obscrvntioiis and ineasurement
of pial ressels. Arch. Neurol. and Psycliiat., 19 : 751-761.
FRIEDBXANN,
U. l942 The blood-brain barrier. .Phvsiol. Rcr., 22: 125-145.
HULRTAS,J., AND F. M. FORSTEK
1951 Pharmacodpamic l.eSlJ01lSCS of pin1
~essels. Frd. Proc., IS: 72.
MINARD,D. 1950 .Fluorescein studics of circulation time in inoilkeys with the
lucite calvarium. Naval M cdical Hescareh lnstitnt,c, Project N Sl 007
081.07.01.
MINARD,l)., AND 8.B. HOWELL 1949 A modified p r o r d u r o for the prtyxmtioii
of the lucite cnlvnriuni in inonkeys. Kav;il JIcdic:il Resc;lrrll Institute,
Project NM 013 012, Report No. 3.
MINARD,D., AND R. F. OSSERMAN 1950 A recording automatic syringr for
rapid intrax-enous injections a t rcgulntrd rates. Sara1 Mcdicnl Xes e n w l i Iiistitute, Project N M OOT 0R1..07.05.
MINARD,I)., E. F. O s s ~ a ~ AAnN D M. EI(TIER1950 A recording t\vo-chnnnel
phot.ofluoromctcr f o r iw eico studies with fluorescein. Naval Yedic.al
Besearch Institute, Projcct NM 00; 081..07.06.
OSSKRXIAN,
E. P., A N D D. M m m n 1.952 A4one-inch lucite craiii;iI window :ind
vit:tllium holder f o r instal1:itioii i n iiionltr.ys. Naval Mrdic:rl Rese:irch
NM 00’7081.07.07.
I n s t i t u t . ~ 1’ro;ject
,
l’EDRNZ, It.. IT., AND C. 1%.SIIELDEN 1945 Tho 1ucit.c ettlvnrimn -$1 met.hod f o r
direct obserrntion of the brain. 11. Cwninl t,rnum:i :rnd l m i n move.
nicnt. J. Neurosurg., 3 : 487-505.
SHELDEN,
C. H., R. H. P~JDENZ,
J. S. RESTARSKI
A X D W. M. CRAIG 1914 Thi:
lueite calvarium -a inctliod f o r direct olmrvation of the 1)r:iin. 1.
The snrgicnl a n d Incite processing tecliniqiies. J. Nemosurg., I : 67-717
SOIILICR,
T. I.’., G. N. LOTHROP
S Y I ) H.S. PORHES
1911 The pi:tl circulation of
normal, non-nncsDhetizcd aninials. P a r t I. Dcseript.ion of R met.liod
of olmerration. .J. Pharniacol. and EqI. l’herap., 71 : 32.5-330.
SPITZ,E. P,. 1947 Pcrsonnl roniiriiinicstioii.
T Z ’ m i ’ s L m , K. E. 1.936 Microscopic ~ t i i d yof siiporfici:il ccrclir:ll vessels of the
rabbit by nieans of a pcriiia iimtly iii~t:iIl~(t
transparent cranial clininl~er.
Annt. Rep., 6 6 : 423-435.
PLA4TE 1
EXPLAN 4TION O F F I G C R E S
Preliaration of tlic liicitc cal\ ariiini in monkeys
Second stage operation. The grooved tieonium ling
skull. X 1/3.
19
bemg iniplauted
011
Third stage operation. Ring implanted 4 01 more weeks preJiouslv. Bone 1s
heing r e n i o ~ e dfiom wiudoiv aieas. I h i a and hone iidge a r e lcft intact. An
impressiori is made a t this stage for usc in molding tlic lacite plate. X 1/3.
Fourth stage operation. One mcek after prei ious operation. The dnra has
been resected and the calraiiurn is being fitted over rxposetl hraiu. The
c:rlrarinm is then bolted t o the ring, the gioove :ind bolt liends sealed, and the
scalp reseetcd. X 1/3.
4 Hcliem:itic sagittal section shoning ielntions hetuecn the lucitc plate,
arid the bonc. X 4/5.
the,
1
iug,
Preparation of the one-inch wiiidom
5 Components of thc ring a n d window assembly, 1. t o r. : ritallium ring;tlireatled
lucite windon-; protecting c a i ~
; and spaiiiicr wrench (for inserting and rcmoving window). X 1/3.
6
Read lioldcr with skull in positioii of head. Cutter arid its adjustable sopports are shown. X 1/7.
7
One-inch vindow with protecting cap 20 d:iy after iustallation. X 2/5.
8
Uose-up of same preparation TTith cap remorrd.
328
X 6/5.
THE LUCITE CALVARIUM IN MONKEYS
PLATE 1
D. MINARD, E. F. OSSEXMAN AND S. B. HOWELL
329
PLhTE 2
EXPLAN ITION OF F'IGl!RES
C l r n n g c ~nit11 tiiiic. in the lucite d w i r i i i m (monkeg no. 6). X
9
4
1)o~s:ilview of cnlr:irium 2 2 days after completion. The l i i r i d is clcnr and
t.liere :ire only sni:ill are:is of fibroiis tlliekcning.
I0 L:itc:rnl view on
s:iiiie
date.
11
. Thew is iilgrowtll of fibrous tissue f r o m
1 ) o r w l ricw of c:ilwriiirn :it 39 d
tlio wiiidow innrgiiis :i11(7 wscularization of anterior one-third of bone ridge.
7~'luicl r(:iii:iiii~ clc:ir : i n d sin:ill rcssels distinctly visihle i n most ~ ~ C R S .
12
1)ors;tl ricw of ca:il\-:iriiiiii 1.75 (1:i;J.s nftrr conipletioll. A loculizrd arca of
infection was srieecssfully treated tlirec months prcvioiisly. No signs of infcction :it this tinir. Note extcnt of bone regeiierntion f r o m airterior one-third
of I)oiir ridge. A port ion of t.lie r e g e n c r a t d fibrous t.issiic niemhrnne was
siil)srqiic~iitlyreswtrcl rrstoririg visiliilit,y of iinderlyiiig pial ressels.
( ~ i i i ~ ~ ~ l l o t u ~~t.coiding
~ t ~ i ~ l ) iof
c the passage of fluoreseein tllroitgh the sinface
of the 1)rniii t'ollowiiig tlic injection of 1.0 1111 j'?& sodium fluorescein i n
leg L v i i i . hIonh(y no. 6 firc days after completion. Right window arra ( r d e r l o
fig. 9 ) . I.'iltcred T'-V illlimin:ltion (G.E. CH-4). 35 mm Eastxian Photoflure film.
.50 mii f 1..? Ions with corning No. 3381 yellow filter. Camera speed 1.8 frames
per second. O r e r i l l ni:igiiifie:rtion x 1.8. Frnincs and timrs bclom nre con11ted
froni initial :ippr:ir:incc of (1-e in pial arteries.
T(WRC~S
13
Silt11 fr:ime (1.93
not yet I,egnn.
.). -1rterial t i r e i m v well filled b u t venol~splinsi. has
14 Tenth fr:iine (2.08 sec.). T h e dye now outlines n
11 fliiorcsceucc is fncling.
15
Siutcciitli frame (3.33 scc.) . Tlic niedi~unw i n s
aiid sintill Icins Ii:ire 1:irgcly faded.
1 (i Twent?-siitli
:I
ilriisc.
network of small
re now outlillcd. Tlic arterieb
fi:iiiie (5.4 wv.).
Late r r n u u s ph:isc~. Only tlic major T-eins
slioir strong flnorescencc~. 'l'lic :irteries and smnllcr \eins arc 110 longer risible.
330
I’LSTE 2
THE LUCLTE CALTAIRIL~Al1N X O K l < E P S
D. N I K A R D , I.F. OSSEBXAN AND S. I(. HOWELL
331
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large, installing, direct, small, method, calvarium, removable, brain, windows, fixation, monkey, lucite, observations, modified, indirect
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