( 310 ) 



Then we have : 



to, = o), + 2n.-r {n ^ 0) 



a>2 = 2l:rr 



Hence w^ = 2nrr {n > 1), so that inside ^l-V tiiere would have to lie 



an invariant point. 



With this we have completely proved the following 

 Theorem. For a continuous one-one tmnsformation with invariant 

 indicatrix of a two-sided surface in itself a circular continuum with 

 two separated invariant complete circumference segments contains at 

 least two ijivariant points. 



E R R A T A. 



In the 3'f^ communication on this subject, these Proceedings Vol. Xill 



p. 767, 1. 6 from top for: indicated, but read: indicated but 

 1. 20 from top for: paraboli read: parabolic 



Physiology. — C. A. Pe,kelharing reads a paper on: '' The excretion 

 of creatinin in man under the influence of muscular tonus'', 

 after experiments b}^ Mr. J. Harkink. 



(Communicated in the meeting of September 30, 1911). 



Some time ago I reported here on an investigation by Mr. Van 

 Hoogenhuyze and myself, proving that in vertebrates the content 

 of creatin in the voluntary muscles increases during the tonus, but 

 not during simple contractions of the muscles. We may therefore 

 expect that by increase of the muscular tonus more creatin passes 

 into the blood than in other circumstances. Moreover a later inves- 

 tigation showed us that creatin, when gradually introduced into the 

 circulating blood, is partly excreted by the kidneys as creatinin '). So 

 we may conclude that an increased tonus will lead to a larger 

 excretion of creatinin. 



A series of estimations by Van Hoogenhuyze and Verploegh 

 showed indeed that less creatinin is excreted per hour during the 

 night when the muscles as a rule are relaxed in sleep, than in the 

 daytime, when the muscles are now in a tighter, now in a less 

 intense tonus. Besides they stated that a smaller amount of creatinin 



1) Onderzoekingen Physiol. Laborat. Utrecht, 5de R. XI. p. 236. 



