1297 
roform 1:500000, Propionic acid 1:10000000) they restrict their 
action to the lipoid surface, which they weaken thus facilitating 
the amoeboid motion. 
When applied in somewhat greater quantities a second factor 
becomes of importance viz. the noxious effect of these substances 
on the protoplasm. All these substances indeed penetrate easily into 
the cells, thus causing paralysis. 
3. Soaps, such as propionate, butyrate and formiate. These sub- 
stances, unlike the fat dissolving substances, do not enter into the 
phagocytes. Their action upon the phagocytes is therefore entirely 
different from that of the fat-dissolving substances, for even when 
applied in high concentrations (1:250), in concentrations in which 
the fat dissolving substances would inevitably kill the cells, they 
have a very favourable effect upon phagocytosis. 
When applied in still greater quantities their action is a perni- 
cious one, but this may be due to the solution being too hyperiso- 
tonic. 
Further it is a remarkable fact and in this respect the soaps 
are distinguished from calcium as well as from the fat dissolving 
substances — that within rather wide limits, the degree to which 
phagocytosis is promoted is independent of the amount of soap, 
found in the solution. (Cf. Tables Il’ and IV.) 
The researches, described above, have given rise to different 
questions, which, owing to the present circumstances we cannot 
enter into now. 
Physiological Laboratory. Groningen, January, 1913 
y J gen, 4 
Astronomy. — “A proof of the constancy of the velocity of light’. 
By Prot" W .: pe SITTER. 
(Communicated in the meeting of February 22, 1913). 
In the theory of Ritz light emitted by a source ‘moving with 
velocity w is propagated through space in the direction of the motion 
of the seuree with the velocity ¢ + x, c being the velocity of light 
emitted. by a motionless source. In other theories (LORENTZ, EINSTRIN) 
the velocity of light in always c, independent of the motion of 
the source. Now it is easily seen that the hypothesis of Rrrz leads 
to results which are absolutely inadmissible. 
Consider one of the components of a double star, and an observer 
situated at a great distance A. Let at the time ¢, the projection of 
