24 Proceedings of the Royal Physical Society. 
may escape, or with any poisons that have not been compelled 
to.act in the caseating area, and to give rise to a quantity of 
new fibro-connective tissue, which may form a localising zone 
—i.e., just as in the case of tubercle undergoing healing 
under normal condition. All this points, as I have said, to 
the fact that Koch is dealing with a soluble poison very 
similar in nature and composition to that set free by the 
tubercle bacillus itself. 
The chemical side of bacteriology is rapidly becoming one 
of the important questions of the day; Roux and Yersin’s 
work on the diphtheria poison, which they have been able to 
separate from cultures of the diphtheria organism, and even 
from the membranes of the throat in which the organism has 
been developed, is a substance which they compare to an 
enzyme. Similar researches have been made on the tetanus 
poison, from which it is proved that the poison here is also of 
the nature of an enzyme, and that its virulence is very great, 
and the recent work on the albumoses and their effects in 
stimulating the cells of the body, and interfering with the 
development of organic poisons, might occupy this Society, 
and probably will occupy some of its members, for years to 
come. This, also, though a most fascinating subject, must be 
left for the present. 
We have been engaged so long and so closely in the study of 
vegetable micro-organisms, that those on the other side of the 
border-land, the animal micro-organisms, are in danger of 
being overlooked, but more light is daily being thrown on the 
action of these latter organisms, and by a process of elimina- 
tion we have been led to think that in those diseases in which 
it has been found difficult or impossible to separate vegetable 
micro-organisms, and assign to them a causal relation to such 
diseases, psorozoa or psorospermze may play a part. The 
coccidia or micro-sporidia described by Pasteur in pebrine, 
or silkworm disease, the beautiful organism found in the 
blood in certain stages of malarial attacks, the psorosperms 
1 Since this was read Koch has made known the composition of his lymph, 
and has added many new facts to our knowledge of its action, but the 
above description, though founded on imperfect data, may still be held as 
essentially accurate. 
