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ó.v^ öy^ öz^ 



and further according to tlie differential equation 



{R — 1) z^ ai3 — Ry^ «7 + -^'i ?y must be equal to 0. 



The two rajs of the complex in the tangential plane have but to 

 be made to coincide. The condition is : 



-4.R{R-\)z,y, f\ /; =z [- (i2 _ 1) z, h + Ry, f\ + ƒ, .^^]^ 



where /i, /j, /g represent the differential quotients of ƒ according to 



X, y and z respective!}', whilst analogous relations are easy to deduce. 



From this ensues that the required curve is the intersection of 



f{x,y,z)^() 

 and 



-4.R{R- l)zyfj, = [- {R - 1) z f, + RyA +A -^T- 

 Without entering into further details I only wish to observe that 

 when f{x,y,z) = represents a plane, the curve can be nothing 

 but the conic of the complex. From the above mentioned equations 

 we therefore find a parabola (the conic of the complex touches the 

 tetrahedron plane at infinity) touching the three planes of coordinates 

 of the rectangular system of axes. 



Physiology. — "On the excretion of creatinin in man". By C. A. 

 PEKEiiHARiNG. Report of a research made by C. J. C. Van 

 HooGENHUYZE and H. Verploegh. 



As the muscle tissue in herbi\'ora as well as in carnivora always 

 contains a not unimportant amount of creatin, and creatinin is daily 

 excreted with the urine it may be concluded, that creatin is formed 

 as a product of metabolism in the muscles, and having entered 

 the blood is at least for a part excreted by the kidnej^s in the form 

 of the anhj'dride, creatinin. 



But no agreement has been obtained about the question whether 

 the forming of creatin is bound to the labour, the contracting of 

 the muscles. To answer that question, researches have been made 

 whether the amount of creatinin excreted by the kidneys augments 

 after muscular labour. Different investigators have obtained different 

 results. Van Hoogenhuyze and Verploegh have resumed the research 

 anew, using a new method to determinate the amount of creatinin 

 in the urine, which was published some time ago by Folin ^). The 



1) Zeitschr. f. Physiol. Chemie, Bd. XLI, S. 223. 



