The Facts of Sex in Relation to Metabolism. 277 
that a Bacterium has a certain physiological effect on cells 
with which it comes into close vital relations. That we 
cannot definitely explain the nature of the fertilisation- 
stimulus, in which we believe, is hardly an argument against 
its existence. We are also at a loss to express the nature 
of the relation between nucleus and cell-substance, the 
importance of which no one doubts. 
We have said that Weismann’s essay abounds in hypothesis. 
As his theory is attractive, it may perhaps tend to caution if 
we bring together a few of these. 
(a) It is not by any means certain that the chromatin 
rods are quite so unique in their importance as Weismann 
and many other biologists constantly assume. “Everything 
which occurs in the cell, including the rhythm and the 
manner of its multiplication, depends upon the nuclear 
substance’””—is a conclusion which appeals to our ignorance. 
We know so humiliatingly little about such matters that 
we hesitate in accepting a large theory, one of whose 
postulates is that the chromatin rods have a monopoly of 
importance. Is it not likely enough that the morphologists 
of the cell, in discovering a substance which responds to their 
stains, and whose behaviour can be watched, have exaggerated 
its importance and depreciated that of less conspicuous 
elements? Does not the recent discovery of the central 
corpuscles, with their attractive spheres, lead one to 
be extremely cautious in fixing the essential qualities of 
life in any one visible structure? Of course it is open 
to Weismann to say, as he does, that the centrosomata 
may be controlled by germ-plasm, and that they may be 
derived from the nuclei. But there is no end to such 
' may-be’s. He urges, moreover, that even if the centrosoma 
be part of the cell-body, its activity depends upon the 
internal conditions of the cell, which “is primarily deter- 
mined in ail its qualities by the nuclear substance.” But 
this last clause is precisely what has to be proved, else the 
contention is simply an argument in a circle. Nor can we 
forget that there is more in the nucleus than chromatin rods, 
and more in the cell-body than a centrosoma, and that even 
