THE RECOGNITION OF THE FOURTH DIMENSION. 189 
exist 12,000,000,000 biophors, or ultimate particles of living 
matter, a sufficient number to account for hereditary trans¬ 
mission, and observes: “ Thus it is conceivable that vital ac¬ 
tivities may also be determined by the kind of motion that 
takes place in the molecules of that which we speak of as 
living matter. It may be different in kind from some of 
the motions known to physicists, and it is conceivable that 
life may be the transmission to dead matter, the molecules 
of which have already a special kind of motion of a form of 
motion sui generis .” 
Now, in the realm of organic beings symmetrical struc¬ 
tures—those with a right and left symmetry—are every¬ 
where in evidence. Granted that four dimensions exist, the 
simplest turning produces the image form, and by a folding 
over structures could be produced, duplicated right and left, 
just as in the case of a plane. A symmetrical and life-like 
contour is created by the child’s amusement of folding an 
ink-spattered paper along the line of blots. 
Whether four-dimensional motions correspond to the 
physiologist’s demand for a special kind of motion or not, I 
do not know. Our business is with the evidence for its ex- 
sistence in physics. For this purpose it is necessary to ex¬ 
amine into the significance of rotation round a plane in the 
case of extensible and of fluid matter. 
Let us dwell a moment longer on the rotation of a rigid 
body. Looking at the cube in Fig. 3, which turns about the 
face of A B F E, we see that any line in the face can take the 
place of the vertical and horizontal lines we have examined. 
Take the diagonal line A F and the section through it to 
G H. The portions of matter which were on one side of A F 
in this section in Fig. 3 are on the opposite side of it in 
Fig. 8. They have gone round the line A F. Thus the ro¬ 
tation round a face can be considered as a number of rota¬ 
tions of sections round parallel lines in it. 
The turning about two different lines is impossible in 
three-dimensional space. To take another illustration, sup¬ 
pose A and B are two parallel lines in the x y plane, and 
