( 688 ) 



ill the usual manner. On microscopic examination the blood-vessels 

 were found to be tilled now loith a per/ecili/ how 0(/eneoiis black mass. 

 This method has an advantage over that of Grosser in the fact 

 that we need not fear the injection-fluid becoming solidified before 

 the injection; besides the preparation of the suspension requires ??iz«c/i 

 less time. 



In another direction too we have simplified the method, viz. by 

 substituting blood-serum for egg white. A mixture of 3 parts of 

 blood-serum with 2 parts of the above named Indian ink gave ex- 

 cellent results. 



The blood-serum need not he denxed from the same species of 

 animal. For injections of caviae or rabbits we got good results In- 

 using horse-serum or cow-serum, fluids that are easily obtained. 



Here too fixation was brought about by means of sublimate-formol. 



As yet kidneys and liver were microscopically examined. But the 

 injection fluid also penetrated skin, muscles and brain. 



An attempt to prepare suspensions of carmine grains in serum 

 suggested itself now, but these experiments failed as the carmine 

 particles conglomerated. Perhaps, however, mixtures of dissolved car- 

 mine or of colloidal fluids may be prepared with serum, giving 

 good results. 



The aliove mentioned experiments were made in cooperation with 

 Mr. A. F. De Boer and Mr. G. A. Kai.verkamp, medical students. 



Gronim/en, March 1908. 



Mathematics. — "The sections of the net oj measiire-polytopes M» 

 of space Sp„ loitli a space Spn—i normal to a diagonal.'' 

 By Prof. P. H. Schoute. 



1. In the first part of a communication on fourdimensional nets 

 and their sections by spaces {Proceedings, Febr. 1908} we have i.a. 

 transformed the net (Cg) into a net (CiJ and a net {C^^); so here 

 the regular simplex, the fivecell C^, was not considered. Whereas 

 the regular simplex of >Sp,, the equilateral triangle, furnishes a plane- 

 filling all by itself as well as in connection with some other regular 

 polygons, and the regular simplex of Sp^, the tetrahedron, can fill 

 the space in combination with the octahedron, it is impossible, as 

 was shown in the quoted paper, to find for the regular simplex C^ 

 of Sp^ other regular cells, which can together fill the space of Sp^. 



This leads us gradually to the question, whether it is not possible 



