ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
35 
cell it may be that only one is visible. But there is often a third little 
body — an accessory corpuscle — or there may be two. These, with the 
centrosomes, are imbedded in an achromatin substance in the centre of 
the astrosphere. This structure, which binds the centrosomes in organic 
unity (“a primary centrodesmosis”) is the microcentrum. The author gives 
statistical tables showing the size-relations and numerical relations of 
the parts of the microcentrum in 1000 lymphocytes; thus 74*6 per 
cent, have centrosomes of unequal size, 19 * 1 have equal centrosomes, 
and in 6 • 3 there are three corpuscles without an accessory corpuscle dis- 
tinguishable as such, for its presence is not constant. The substance 
included in the primary centrodesmosis is the material from which the 
central spindle is formed by assimilation, growth, and differentiation ; 
it is the rudiment of the central spindle in the resting cell, and the 
accessory corpuscles are minute extra centrosomes. During rest, one 
or two centrosomes may be formed anew, by a process comparable to 
budding. The microcentrum is an organ which pursues its course of 
development to a certain degree independently of mitosis. 
The second chapter discusses the position of the microcentrum and 
the polymorphism of the nucleus. The polymorphism only occurs when 
the volume of cytoplasm is relatively little when compared with the 
volume of the nucleus. A large proportion of the cellular threads (the 
fila of the mi tome) are centered as radii around the astrosphere ; they 
are the organic radii of the cell ; the microcentrum is their point of in- 
sertion. All the radii are supposed to have the same number of micro- 
somata, and it is supposed that under equal strain they are of equal 
length. What Heidenhain seeks to show is that the relative positions of 
microcentrum, nucleus, and masses of plasma, as well as the polymor- 
phism of the nucleus, are interpretable in terms of varying tension in 
the mitome. . 
The third chapter criticizes Flemming’s attempt to deduce a “po- 
larity ” of the cell from the presence of two centrosomes. Heidenhain 
finds that Flemming’s so-called cell-axis — drawn through the two 
centrosomes — is quite inconstant, and he dismisses this conception of 
polarity. 
The fourth chapter discusses the final movements of mitosis (telo- 
phases, telokinesis). They also are interpreted in terms of the tensions 
of the mitome threads. The fifth chapter deals with the structure of 
the nucleus. The framework consists of a fundamental substance 
(linin) with spherules (microsomes) of the size of centrosomes im- 
bedded in it. The author distinguishes oxychromatin (or lanthanin) 
with a special affinity for acid anilin stains (rubin S) from basi chro- 
matin with a special affinity for basic anilin stains (Biondi’s methyl- 
green). All nuclei show this double reaction, but the two substances 
occur in intimate juxtaposition ; oxychromatin is probably nuclein poor 
in phosphorus, while base chromatin is rich in phosphorus ; the diverse 
affinities of the microsomes probably vary in an unknown way according 
to the metabolism of the nucleus and cell. 
Herr Heidenhain then passes to the megacaryocytes, the giant-cells 
of the medulla. The sixth chapter describes their form and nuclei. 
The concentric layering of the cytoplasm is very characteristic, and is 
the subject of the seventh chapter ; there are three layers in the ecto- 
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