SECTIONAL TRANSACTIONS.—I. 461 
becoming more and more evident that a clinical entity may not be caused by a single 
agent. For instance, some virus maladies are induced not by one virus but by two, 
while others appear to be produced by the concerted action of viruses and bacteria. 
Therefore the fact that visible bacteria are consistently found in certain virus diseases 
does not mean that they are always harmless secondary invaders, nor does it necessarily 
indicate that they are the visible form of the viruses. At present there is no conclusive 
proof that viruses are filterable forms of bacteria. 
The pathological pictures observed in virus maladies have an indirect bearing 
upon the nature of the agents inciting them. Cells injured by many viruses frequently 
exhibit inclusion bodies, concerning the nature of which numerous conflicting opinions 
exist. In some diseases, such as wilt of caterpillars, there is evidence that the infective 
agents are not associated with their characteristic inclusions, while in others, such as 
fowl-pox, large amounts of the viruses are undoubtedly present within these structures. 
In spite of definite proof that viruses are present in certain types of inclusions, there 
is still doubt regarding the organismal nature of the small coccoid bodies of uniform 
size found within them. 
Other features, hyperplasia and necrosis, observed in the pathological pictures 
induced by viruses are fully as important as are the inclusion bodies, and it is because 
of them that such phenomena as lysis of bacteria, fever blisters, smallpox, warts and 
tumors can be discussed logically at the same time. Such a statement naturally opens 
up the question of the etiology of malignant neoplasms. Undoubtedly a number of 
fowl tumors are caused by agents separable from cells, and, although there is as yet 
no proof that human cancer arises in this way, the possibility is one that must be 
seriously considered, and offers a fertile field for work. The fact, however, that some 
tumors are produced by filterable agents is by no means conclusive evidence that 
all neoplasms arise through the activity of such agents. 
_ Dr. J. Henperson Surta.—Plant Viruses. 
The viruses which occur in plants have essentially the same characters as the 
animal viruses. They have the small size, the capacity for indefinite multiplication 
and spread, the infectivity, the inability to increase in the absence of living cells, the 
production of intracellular inclusions, the differences among themselves in specificity 
and resistance, and so on. There are differences in effects, e.g. plants are unable to 
develop an active immunity; but there is no doubt that in their nature they are 
similar to the animal viruses. What that nature is remains equally uncertain. The 
relevant evidence is of the same kind, e.g. for the small size the microscopic invisibility, 
and the results of differential filtration. The latter method, however, can give no 
precise data at present as to the exact dimensions, since ability to pass an orifice is 
dependent as much on capacity for distortion as on actual size, and we have no 
information as to the rigidity of the virus particle. In at least one case it seems 
definitely established that the intracellular inclusions are formed by the aggregation 
of particles of altered cytoplasm. 
_ Exact quantitative data are deficient on the plant side; and it is only recently 
that it has become possible satisfactorily to free the viruses from the other ingredients 
of the plant juices and isolate them in a relatively high degree of purity, which is 
an essential preliminary step. 
There is no fact certainly established which is incompatible with the organismal 
hypothesis ; and some which seem more easily explained on such a theory than on 
any other. It is certain, for example, that some of the plant viruses multiply in their 
insect vectors, and that there is in some cases an interval during which the insect after 
infection is not capable of transmitting the disease, the so-called incubation period. 
Again, in some commercial crops, e.g. sugar-cane, millions of plants are grown annually, 
in which unlimited opportunity is given for abnormal cellular constituents to originate, 
ut virus disease does not appear, unless it is introduced from without ; and its rapid 
ad, when so introduced, shows that, if an infective cellular abnormality did arise, 
it would reveal itself. The analogies for the parasitic view are very strong, and while 
it must be recognised that there is as yet no definite and conclusive evidence one 
or the other, it seems more reasonable to adopt provisionally the position that 
le plant viruses are parasitic organisms, not necessarily bacterial or protozoal or 
them, but with special characters imposed by the small size. 
Dr. R. ALEXANDER. 
