1467 
pencil consists of the intersection of two of the planes c, c’, c’ and 
a cubic lying on ®*. So the /* on w° is determined by a pencil of 
conics 6°, of which three base-points S,, S,, S,, lie on w°. A qua- 
dratie transformation with principal points 5, transforms w* into a 
curve x° passing through Sj} and the pencil (6°) into a plane pencil, 
of which the vertex S* lies outside °. The six tangents sent by z° 
through S* are the images of six conics o° touching at y*; the 
plane w is therefore touched by szz curves 9°. The congruence |r| 
of the tangents at the curves 9° has therefore the class sia. 
If a plane yw is laid through the singular point C, the involution 
/*. degenerates into an involution /*, the pairs of which are com- 
pleted into triplets by C. Of the six tangents 7 four pass through P ; 
the remaining two are replaced by the straight line touching the 
curve 2° in C. 
§ 6. The congruence [7] has the planes cj of the conics 9%; as 
singular planes. The tangent plane o, in C at ®° is also singular, 
for every straight line of the pencil (C,6,) is tangent at a Q*. C is 
of course at the same time singular point of [r]. 
Through a point P of ®° pass five tangents 7, viz. the four tangents 
of 2°, having P as tangential point, and the straight line 7, which 
touches the 9° laid through P; this tangent must be counted twice. 
The order of [r] amounts therefore to sr. 
The straight line f, is intersected in the pairs of an /* by the 
curves 9°; it is therefore tangent for two of these curves, so that 
the osculating planes w of the two points of contact pass through /,. 
The line /, further bears the plane 6,, which must be considered 
as osculating plane of the conic 9,*. As each of the three planes 
mentioned must be counted twice, we may conclude that the osculat- 
ing planes of the curves 9° envelop a surface 2 of class six. 
For the figure (@,’,g,) the straight line /,, touching o,* in its 
intersection with g,, is triple class axis, 2 contains consequently the 
sia straight lines hy. 
Pathology. — “The influence of feeding and of starvation on the 
development of polyneuritis gallinarum”. By Prof. Dr. ©. 
Evkman and Dr. C. J. C. van HOOGENHUYZE. 
(Communicated in the meeting of February 26, 1916.) 
As communicated by me in 1896 Dr. A. G. Vorperman undertook 
an investigation, into the relationship of the nature of a rice-diet 
with the occurrence of beri beri in the prisons of Java. These 
researches had been suggested by my studies of polyneuritis galli- 
