( Ö2J ) 



§ 7. The curve of inflections (/) and tlie bitangential curve (Z)) 

 have in each of the 3 [n — 1)'' nodes of (''") in common a number 

 of 2 (n — 3) {n + 2) points. 



For, out of a node we can draw to the c" to which it belongs 

 («' — n — 6) tangents, to be regarded as double tangents, whilst e^eli 

 node of a c" is at the same time node of (/). 



In each basepoint lie moreover 3 (« -|- 4)(/i — 3) points of inter- 

 section (§ 4). The remaining points common to (D) and (/) are 

 the inflections of which the tangent touches the c once more {^ 4) 

 and the undulation-points {^ 6) where the two curves touch each 

 other. 



Indeed, we have 



ö(n — lf {n - 3) (« + 2) -f 3h' (« + 4) («— 3) +" 3 {n - 4) («—3) (n'^6n—i) + 

 4- 12(« — 3)(3« — 2) = 6{h — l)='(n— 3)(«+2) + 3(/(— 3)(2«'+(3«'— 1(3/(+8) — 

 = ti(n-l)(H— 3) (2«'-f 5«— 6), 

 and this is the product of the orders of (/) and (D). 



Physiology. "0« the strength of reflex stiimiU an weak an jjonnHik." 

 By Prof. H. Z\va.\rdemaker. (Report of a research made by 

 D. I. A. VAX Reekcm). 



(Communicated in the meeting of March 31, 1906). 



Investigated were chemical, thermal, mechanical and electrical 

 stimuli, which partly acted upon the skin partly on the sensible nerves 

 of the animals, wliich were experimented on. 



§ 1. The chemical stimuli were applied by immerging tlie hind- 

 leg of a winterfrog in a little bowl with a solution of sulphuric 



acid varymg from V „ to V„7„ ( ^ *» — 1. The spinal cord system 



was withdrawn in the usual way from the influence of the cere- 

 brum. After the experiment the legs were washed with distilled 

 water and the experiment repeated after a pause of 5 minutes. 

 Neglecting the preliminary reflex, only a complete reflex was consi- 

 dered as a positive result. After-reflexes and general movements did 

 only show themselves when rather strong concentrations were used. 



As a rule a \i;°/(,(~) solution of sulphuric acid may be accepted 



as the minimum stimulus which still pi'oduces reflexes. The reflex- 



