TRANSACTIONS OF SECTION K. 565 
cytoplasm which lead to the appearance of a fibrillar structure in the form of 
a more or less regular spindle, the threads of which come into contact with the 
chromosomes through the breaking down of the nuclear wall. The chromosomes 
then, by the action of a force or forces of which we as yet know very little, 
arrange themselves in regular order in the equatorial plane of the spindle figure, 
and some of the spindle fibres become attached to them. The chromosomes 
become divided longitudinally into two apparently exactly equal halves; and 
then, probably by the exertion of some sort of contractile force or pull on the part: 
of the spindle fibres, the separate halves are caused to move to opposite poles of 
the spindle. Here a series of transformations take place, which lead to the 
constitution of two new nuclei. Such are the essential features in this complex 
process of nuclear division, and it is a striking fact that they occur with more or 
less regularity jn all nuclei from the alge and fungi up to the highest plants. 
The Structure of Cytoplasm. 
‘In the elucidation of cell structure we owe much to the beautiful methods of 
staining and fixing which are due especially to Flemming and Heidenhain, to the 
improved micro-chemical methods which we owe especially to Zacharias and 
Macallum, and to the investigations of such observers as Fischer and Mann, who 
have shown us the effects of various reagents upon the living substance, and have 
thus taught us to be very cautious in our interpretations of the structures seen in 
dead fixed cells. 
The investigations of oil-foams and colloids by Butschli, Hardy, and others 
have given us a clue to possible explanations of the various appearances seen both 
in the living and dead fixed and stained cells, and the introduction of the ribbon 
section cutting microtome into the domain of vegetable histology has enabled us 
to male the best use of the beautiful apochromatic object-glasses which we owe to 
the researches of the late Professor Abbé. 
It is unfortunate that, so far, very little progress has been made in the exami- 
nation of the structure of the living cell. We may hope that, with the improved 
methods of illumination now available, combined with experimental investigation, 
it will be possible to make some progress in this direction. It is of the greatest 
importance that we should be able to satisfy ourselves to what extent the various 
appearances seen in the fixed and stained cell are due to the action of the reagents 
employed. In this respect a recent discovery by Kohler, which indicates the pos- 
sibility of making use of the ultra-violet rays in such investigations, is of interest. 
Kohler (‘ Phys. Zeit.,’ 1904) finds that if the ultra-violet rays from the electric spark 
between cadmium or magnesium terminals are separated out by means of quartz 
prisms, objects illuminated by them, when examined by means of lenses made of 
quartz, show differentiations of structure which otherwise require staining to make 
them visible. The chromatin of the nucleus and such substances as cuticle and cark 
are almost opaque to the ultra-violet rays, and can be made visible on a fluorescent 
screen or can be photographed. The resolving power of the microscope is doubled, 
and Lummer considers that the principle employed is the only one by which 
further progress in resolving power can be made. If the method is found by 
eytologists to be a workable one, it may open up an entirely new field of micro: 
scopic investigation by which the protoplasmic differentiation in living cells may 
be more clearly revealed. 
Many attempts have been made to show that the cytoplasm possesses a definite 
morphological structure of its own, which is related to the various functions it 
performs, and that it is not a formless semi-viscid fluid in which various physical 
and chemical forces are at work, and upon which the various structures observed 
depend ; in other words, that it possesses a morphological constitution as opposed 
to a merely chemical one. 
Fromman and Heitzmann in 1875 described the structure of cytoplasm as con- 
sisting of fine threads or fibres in the form of a net with fluid between and form- 
ing a sponge-like structure. Flemming in 1882 described it as composed of two 
substances, one in the form of fibrils (filar substance) emhedded in the other, 
