(274) 
whole of the dermatoma, will be made clear by the two following 
experiments. 
Experiment of September 22'* on a brown male dog. The medulla 
is laid bare, and the dura mater opened. The originating bundles 
of the 19th, 20th, 21 and 22 posterior roots then were distinctly 
visible. On both sides a few caudally situated bundles of each of 
these roots are cut through, whilst the bundles situated cranially 
are left intact. 
The next day there is found on abdomen and back a not very 
strictly defined hyperalgetic area, corresponding to the extension- 
area’s of the four partly injured roots. Nowhcre however, analgesia 
can be found. 
As counterpart to this experiment, another is made Oct. 22 on 
a white female dog. The cranial bundles of four posterior roots 
(the 17%, 18th, 1yt and 20) are cut through, whilst the cadual 
ones remain intact. 
The result on the next day is again a hyperalgetic area, now 
perfectly well defined, roundabout the trunk, with strong hyper- 
reflectory reaction, nowhere however in that area analgesia can be 
pointed out. 
A few bundles only, may they be caudal or cranial (provided the 
normal conditions of overlapping of the dermatomata do exist), are 
sufficient for the innervation of the whole dermatoma, and make 
sensation possible everywhere. If they are cut through in an isolated 
dermatoma, then sometimes the whole central ares may appear, but 
in most cases those narrowings, resp. transversally divided shortenings 
of that central area, represented in fig. 3, 4, 5 and 6. It must be 
understood withal that as long as one bundle remains intact, at least 
in that part of the dermatoma lying adjacent to ihe back, sensation 
is preserved. 
Astronomy. — ‘Contributions to the determination of geographical 
positions on the West-coast of Africa.” By C. SANDERS. 
(Communicated by Dr. E. F. van DE SANDE BAKHUYZEN). 
I. The instruments used. Determinations of the corrections 
and the rates of the chronometer. 
The hope expressed in my paper, read at the meeting of the 
Academy of January 1900, of soon having at my disposal a small 
universal instrument, by means of which a much higher degree of accuracy 
