80 SECTIONAL ADDRESSES. 
That these factors® must at least be self-propagating substances, 
subsidiary vortices in the main stream of metabolising living proto- 
plasm, is certain, since they grow and multiply repeatedly, to be 
distributed to new generations of germ-cells. That they may be 
relatively constant and remain unaltered for generations seems also 
certain, since organisms or their parts can continue almost unchanged 
for untold ages. That they can act independently, can be separately 
distributed into different germ-cells, and can be re-combined seems 
likewise to have been proyed by the brilliant work of Mendel and his 
followers. So independent and constant do they appear to be that 
modern students of heredity tend to treat them as so many beads in a 
row, as separate particles themselves endowed with all the properties 
of independent living organisms, the very properties we wish to explain 
While not prepared to accept these views without qualification, it seems 
to me that it can scarcely be doubted that some such units must exist 
whether in the form of discrete particles or merely of separable sub- 
stances. But not until these factors have been brought into relation 
with the general metabolism of the organism, as links in the chain of 
processes, will the problem of inheritance approach solution. If the 
theory is to be completed it must attempt to explain how they come to 
differ, how their orderly behaviour is regulated, in what functional 
relation they stand to each other, what is the metabolic bond between 
them. That harmonious processes may be carried out by discrete 
elemenis in co-operation is shown in cases of symbiotic combinations 
such as the lichens, or the green alge in such animals as Hydra and 
Convoluta. Here an originally independent organism takes its place 
and does its work regularly in another organism, and may even be 
propagated and transmitted from one generation to the next in the 
germ-cell! Most instructive, also, are the recently studied cases of 
bacteria and yeasts living regularly in certain special tissues of various 
species of insects, where they exert a definite influence on the 
metabolism (see the works of Pierantoni, Buchner, Glaser). These no 
doubt are mere analogies, but they serve. 
In all probability, then, factors of inheritance exist, and the funda- 
mental problem of Biology is how are the factors of an organism 
changed, or how does it acquire new factors? In spite of its vast im- 
portance, it must be confessed that little advance has been made 
towards the solution of this problem since the time of Darwin, who 
considered that variation must ultimately be due to the action of the 
environment. This conclusion 1s inevitable, since any closed system 
will reach a state of equilibrium and continue ‘unchanged, unless affected 
from without. To say that mutations are due to the mixture or rée- 
shuffling of pre-existing factors is merely to push the problem a step 
6 Herbert Spencer’s ‘physiological units,’ Darwin’s ‘ pangens,’ Weismann’s 
‘ determinants,’ are all terms denoting factors, but with somewhat different 
meanings. More recently Professor W. Johannsen (lemente der exakten 
Erblichkeitslehre, 1909) has proposed the term ‘ gene’ for a factor, ‘ genotype’ 
for the whole assemblage of factors transmitted by a species, and ‘ phenotype ’ 
for the characters developed from them. -This clear system of nomenclature, 
although much used in America, has not been generally adopted in this country. 
