; I.—PHYSIOLOGY. 173 
the centre for report and discussion of all investigations bearing on the 
nature of the life process in the individual, in health or in reaction to 
disease. The present tendency, indeed, is for the creation of new links 
_ rather than new cleavages. We may observe with satisfaction that 
among our colleagues in the sections of botany and zoology the detailed 
study of the vital processes of plants and animals has gradually been dis- 
placing that of form, habit and distribution from the predominance which 
it held in earlier years. Not only the phenomena of the normal life, but 
those also of the diseases of plants, have claimed the attention of our 
botanical colleagues. Functional Biology presents problems sufficient in 
number and interest to occupy the attention of several sections, and it is 
all to the good that different aspects of the same group of phenomena 
should engage the attention of investigators belonging to more than one. 
Particularly welcome is this combined approach to a subject such as that 
chosen for to-day’s discussion, to which my own remarks can only serve as 
introduction. We are to deal with a group of agents, the existence of 
which would certainly be unknown to us, but for the changes produced by 
their presence in the bodies of higher animals and plants. They seem to 
have one property at least of living organisms, in being capable, under 
appropriate conditions, of indefinite reproduction. We know nothing of 
their intrinsic metabolism : it has even been asserted that they have none. 
Few of them have yet been rendered visible by the microscope; it is, 
indeed, a question for our discussion whether any of them have yet been 
seen or photographed. It is a question again for discussion, whether any 
of them, or all of them, consist of organised living units, cells of a size 
near to or beyond the lowest limits of microscopic visibility ; or whether, 
as some hold, they are unorganised toxic or infective principles, which we 
_ can regard as living in a sense analogous to that in which we speak of a 
_ living enzyme, with the important addition that they can multiply them- 
_ Selves indefinitely. Some, however, would attribute this, not to actual 
een etestion, but to a coercion of the infected cells to reproduce 
_ the very agent of their own infection. Since nothing is known of their 
structure or their metabolism, these so-called viruses cannot yet be 
_ claimed as belonging either to the kingdom of animals or to that of plants. 
_ Our colleagues the botanists claim an interest in them, indeed ; but only 
_ because agents having the characters attributed to viruses cause a large 
_ number of diseases in the higher plants, acquiring thereby an added 
scientific interest and serious economic importance. So far as I am 
aware, there is no similar claim for the study of the viruses infecting 
animals and man to be regarded as belonging to Zoology. 
bs Tn this section of Physiology, apart from our wide responsibility for 
_ bringing the British Association into contact with new and fundamental 
“investigation in medical and veterinary science, the problems presented by 
‘the nature and behaviour of the viruses cannot fail to raise questions of 
_ the greatest interest to anyone concerned with general physiological con- 
ceptions. What is the minimum degree of organisation which we can 
"reasonably attribute to a living organism? And what is the smallest 
‘space within which we can properly suppose such a minimum of organisa- 
tion to be contained 2 Are organisation, differentiation, separation from 
