Physiology. — “On Optic “Stellreflexe” in the Dog and in the 
Cat’. By Prof. R. Maenus and A. pr Kieyn. 
(Communicated at the meeting of January 31, 1920). 
In a series of researches carried out in the Pharmocological 
Institute of Utrecht various animals were examined on “Stellreflexe”’, 
i.e. those reflexes that make the animal resume its normal position, 
when it has been brought into an abnormal one. 
‘In the first communication *) “Stellreflexe” in rabbits after extir- 
pation of the cerebrum, were described and discussed in detail. 
The ability of these animals to regain from any given position 
of the body their normal position finds its explanation in the co- 
operation of four different groups of reflexes whose centres lie in 
the mesencephalon. 
These reflexes are: 
1. “Stellreflexe” from the labyrinths towards the head, which make 
the head return from any given position to the normal one. They 
may be best seen when taking the animal by the pelvis and holding 
it up in the air in various positions. 
2. “Stellreflexe” towards the head, provoked by asymmetrical 
stimulation of the sensory nerves of the trunk. 
These reflexes may be best examined after bilateral extirpation 
of the labyrinths. When, after this operation the body lies in 
asymmetrical position on the ground, reflex action will cause the 
‘head to resume its normal position through asymmetrical stimulation 
of the nerves of the trunk. 
3. “Stellreflexe” starting from the neck. 
When the head has obtained its normal position through the 
above-named reflexes, but the body has not, a reflex is elicited by 
the abnormal position of the neck (rotation, flexion ete.) which 
makes the body resume its normal and symmetrical position with 
regard to the head. 
4. “Stellreflexe” towards the body through asymmetrical stimu- 
lation of the sensory nerves of the trunk. 
1) R. Maenus. Beiträge zum Problem der Körperstellung. I. Mitt. Stellreflexe 
beim Zwischenhirn- und Mittelhirnkaninchen. Pflügers Archiv. Bd. 163. S. 405. 1916. 
