PLANT DISEASE AND THE " VICIOUS CIRCLE." 309 
PLANT DISEASE AND THE " VICIOUS CIRCLE." 
By Jamieson B. Hurry, M.A., M.D., 
Author of " Vicious Circles in Disease," 
A Vicious Circle in pathology is denned in Murray's English 
Dictionary as "a morbid process consisting in the reciprocal con- 
tinuation and aggravation of one disorder by another.' ' This process 
plays a r61e of great importance both in animal and in vegetable 
pathology, especially in the higher members of the two great kingdoms 
of living things in which there is differentiation of structure and 
function. 
Throughout life there is a constant process of reciprocation taking 
place between various organs and functions. Thus in animals the 
nervous, the cardio-vascular, the respiratory, the digestive, the renal 
and other systems' are intimately associated with each other, their 
functional activities being harmonized by an all-controlling nervous 
system, increased or diminished requirements in one direction being 
balanced by the necessary adjustments in another. Moreover, a 
swiftly circulating fluid by means of a self-regulating mechanism 
supplies to each tissue the quality and quantity of nutriment required, 
while waste products that would clog further activity are removed. 
The corresponding correlations as seen in plants are less obvious 
than they are in animals. There is neither an all-controlling central 
nervous system, nor a rapidly circulating nutrient fluid at all com- 
parable with the blood. Nevertheless, in principle the phenomena 
of correlation are the same as those in animals/ and are governed by 
protoplasmic stimuli connecting every part of the organism with 
every other part. 
This applies to the shoots, leaves, cortex, cambium, roots — in fact 
to every organized structure, although the inter-dependencies are 
more intimate in some cases than in others. Thus both in animals 
and in plants the vital mechanism is carried on by means of a cease- 
lessly operating chain of complex and reciprocal interactions. 
Even within the limits of health there is frequent disturbance 
of the harmonious co-operation between various organs. Such 
disturbance, however, rapidly provokes reactions which remove the 
source of irritation and restore the natural state of equilibrium. If 
the disorder is too severe to be repaired by physiological reactions 
the condition passes into one of disease. 
Disorder in one organ is then apt to awaken disorder in other 
organs, which in turn reacts injuriously on the first, so that a sequence 
of pathological correlations is established. Thus in the case of the 
animal cardiac disease affects the nervous, the respiratory, the digestive 
