( 635 ) 
Let us now suppose n % to be = 2 n x ; then we get: 
9'i + *»* q\ — c rtj* — b n* + 2 p) q\q 9 , 
9. + n f ? 1 = (2c« 1 s --6 V + p) q\\ 
So we find: 
( <?', 4- 2 d 2 q\ g t =0, 
The equations determining the first approximation have exactly 
the same form as those found in § 4. What was formerly deduced 
for the simple mechanism holds consequently, if iu = 2n x , for an 
arbitrary mechanism with two degrees of freedom in such a sense 
that the horizontal projection of the point moving over the surface 
may be regarded as the representative point for the arbitrary mechanism. 
We finally observe that any mechanism for which 
- 2cV 4- 46V — pz=z0 
is not sensitive for the relation n, = 2n x . So this is the condition 
requisite to make the mechanism for n t = 2n x a mechanism of 
exception in the sense indicated by Prof. Korteweg (§ 26 of his paper). 
Mechanisms of exception therefore are among others the symme¬ 
trical mechanisms (§ 31 of that paper); for here c, b, and p are all 
equal to zero. 
Microbiology. —- “ Viscosaccharase, an enzyme which produces slime 
from cane-sugar”. By Prof. Dr. M. W. Beijerinck. 
' The emulsion reaction. 
Many spore-producing and a few non spore-producing bacilli, cause, 
when growing in presence of cane-sugar or raffinose on neutral or 
feebly alkaline agarplates, a very peculiar “colloidreaction”, which is 
also valuable for the diagnosis of these bacteria. This reaction consists 
in the formation, in and also on the surface of the agar around the 
colonies or streaks, of a liquid “precipitate”, i. e. an emulsion, which 
can best be recognised in transmitted light, and at the same time in 
a swelling of the agar caused by the increase of volume produced 
by the emulsion. 
The emulsion consists of drops (see plate) of different size, mostly 
very small, but sometimes growing to 0,2 mm. so that they may 
