Physiology. — “A Simple Method to obtain a Curve of the Con- 
traction of the M. arrectores pilorum”*). By Miss L. Kaiser. 
(Communicated by Prof. G. van RIJNBERK). 
(Communicated at the meeting of June 25, 1921). 
When placing the tail of a cat before the slit of a camera with 
a vertically moving plate, so that the dorsal side of the tail is 
directed towards the middle of the slit, we obtain on the sensitive 
plate a rather well-defined shadow. When stimulating the sympathetic 
chain, by which process the hairs are elevated, this elevation is 
imaged on the plate as a broadening of the shadow. The outer border 
of this shadow being, indeed, a rather sharp line, it affords a curve 
of the contraction of the M. arrectores pilorum, illustrating various 
features of this contraction, such as duration of the latent period, 
duration and shape of the crescent, ete. as the figure shows. 
By this method I made several records. In all cases the sympa- 
thetic chain was stimulated with the tetanic current of an ordinary 
induction-coil. The curve, then, represents a tetanic contraction and 
not a simple one. We ascertained the average duration of the 
latent period, and its variations by altered strength of the stimulus, 
by fatigue, etc. We also determined the duration and the steepness 
of the ascending part of the curve under different conditions. Finally 
also the height of the contraction was estimated. 
From this height the real shortening of the M. arrectores pilorum 
might be derived. Mr. WOERDEMAN furnished me with some necessary 
data, which he found by measurements in a microscopic preparation 
of a cat’s skin. Let the distance from the insertion of the M. arrec- 
tores into the hair to the turning point of the latter be 400 u, and 
let the length of a hair be 24 ecm., then, at the extremity of the hair 
the magnification of the contraction will be x 60. The projection 
caused an additional enlargement of >» 1.2, so that the entire magni- 
' fication must be fixed at about Xx 75. An average broadening of 
the shadow of 2,5 em, as found in my curves, points, therefore, to 
a shortening of the muscles of 250 u. 
1) After experiments made in the Laboratory for Physiology of the Amsterdam 
University. 
6 
Proceedings Royal Acad. Amsterdam. Vol. XXIV. 
