SEPTEMBER 18, 1913] 
and Prof. Noyons, of Liége, showed curves which 
be believed indicated that there is an antagonism 
between the internal secretion of the pancreas and 
adrenalin. The demonstration by Prof. Magnus, 
of Utrecht, on the influence of the position of the 
head on the posture in decerebrate rigidity and in 
‘normal rabbits was very interesting. The effects 
are in part due to reflexes from the neck and partly 
to labyrinthine reflexes. 
A novelty of great interest to those interested 
painting was the demonstration by Mr. A. H. 
unsell, of Boston. This was a quantitative 
classification of pigment colours based upon 
easurements by a daylight photometer, Maxwell 
discs, and the trained discrimination of the painter. 
The photometer uses the daylight adapted eye, and 
reads in terms of the Weber-Fechner law. 
__A somewhat surprising communication came 
from Prof. Hiirthle, of Breslau, who has made a 
careful study of the variations in pressure and 
velocity in various arteries during the pulse wave 
in living animals, and in dead animals perfused by 
means of an “artificial heart.” From these ex- 
periments the conclusion is drawn that the arteries 
are rhythmically contractile, and that their con- 
traction aids the circulation of the blood. It would 
be interesting to see these experiments repeated 
with a dead animal perfused from a living heart 
prepared according to Starling’s method. 
Many interesting apparatus were shown; among 
_ these may be mentioned the now well-known appa- 
ratus of Prof. Krogh, of Copenhagen, for the 
_ investigation of various respiratory problems; that 
of Dr. Franz Miiller, of Berlin, for the determina- 
tion of the minute-volume output of the heart in 
man by a simple application of the nitrous oxide 
method; the ‘‘Kurvenkino” devised by Prof. 
Straub, of Freiburg, by means of which tracings 
made on smoked glass in the laboratory may be 
_ projected on a screen with realistic effect (appara- 
tus made by Jaquet, of Basel); and the apparatus 
of Dr. Rohde, of Heidelberg, for the measurement 
of the oxygen usage of the frog’s heart under 
Various conditions of contraction. Dr. Laqueur 
also showed a projection method for exhibiting the 
movements of the intestines to a large audience. 
The great event of the congress so far as com- 
munications are concerned was the closing lecture, 
which was given by Prof. Pawlow, of St. Peters- 
burg, on “Die Erforschung der héheren Nerven- 
tatigkeit,” in which he dealt with the subject of 
conditional reflexes, to which he has devoted the 
latter third of his active scientific career. Prof. 
Pawlow is of the opinion that psychology in its 
é 
physiologist. The physiologist must remain a 
Physiologist, and must investigate his problems 
by the recognised methods which have been so 
“fruitful in other fields—he must study the brain 
. an integrated working organ, and must build 
up his knowledge independently of the psycholo- 
gist. The study of reflex action as a purely 
physiological topic has already yielded valuable 
results on treatment by the methods of experi- 
mental physiology. 
work of the Pawlow school that we must extend 
@ NO. 2290, vot. 92 | 
ie 
present condition can be of little service to the | 
NATURE 
| are 
It is rendered clear by the | 
63 
our ideas of reflex action and recognise that 
besides the elementary function of carrying out 
ready-formed reflexes, the nervous system has 
another equally important and fundamental func- 
tion—that of the formation of new reflexes. It is 
a generally recognised property of living organ- 
isms to adapt themselves to their surroundings, or, 
in other words, to respond in suitable manner to 
what were previously indifferent agencies. So far, 
the reflexes which have been most studied by 
Pawlow have been those concerned with the secre- 
tion of saliva in dogs. Various stimuli can be 
given so as to affect different sense-organs in 
different cases, and at the same time the animal is 
fed, or acid introduced into its mouth; after a short 
period of such treatment a new reflex has been 
introduced, for now on application of the accom- 
panying (“conditional”) stimulus alone, without 
the introduction of the food or acid (“unconditional 
stimulus’’), a reflex secretion of saliva occurs. 
Such reactions have all the characters of the true 
reflexes, and are equally simple in character, and 
not, as might seem at first sight, complicated 
processes grafted on to an unconditional reflex. 
The intricacy of the conditional reflex is due not 
to the complex nature of the neural processes 
involved in the reflex, but to the ease with which 
it can be inhibited; innumerable conditions in the 
nervous system itself and in the outer world 
modify it in this way, and thus investigation of 
the phenomena is not easy. In close relation to 
the formation of a conditional reflex is the func- 
tion of the analysis of the sensations which reach 
the organism from the outer world, and from 
which some components are selected by the 
process of analysis; it is only these selected com- 
ponents which are really utilised in the construc- 
tion of the new reflex. It seems, then, that by 
careful study of these reflexes we have the means 
for acquiring an accurate knowledge of the func- 
tional activity of the analysing mechanism. The 
chief problems which have been investigated are 
those concerned, firstly, with the origin of the 
conditional reflexes, and secondly with the mech- 
anism of analysis of sensations. These reflexes 
can be formed in relation to strong as well as to 
indifferent stimuli; thus powerful electric stimuli 
applied to the skin, when the reflex has been 
trained, do not lead to movements of defence or 
aggression as is at first the case, but merely to 
the feeding reflexes of which the flow of saliva is 
the easiest to follow. This is to be explained as due 
to the formation of new nerve paths, determined 
by different excitability of the various nerve centres. 
Thus the stimulation of bone cannot be made to 
yield the conditional reflex, since the centres con- 
nected with painful stimulation of bone are more 
powerful than those connected with alimentation. 
An important condition for the upbuilding of a 
conditional reflex is that the particular conditional 
stimulus used must precede, or accompany, not 
follow, the unconditional stimulus (food or acid). 
If it follows the unconditional stimulus, inhibitions 
set up, and this inhibition has also been 
studied. It is also of great importance that the 
stimulus employed be strictly isolated from inci- 
