VEGETATIVE VIGOR OF THE HOST AS A FACTOR INFLU- 
ENCING SUSCEPTIBILITY AND RESISTANCE TO 
CERTAIN RUST DISEASES OF THE HIGHER 
PLANTS 
I 
M. A. Raines 
(Received for publication July 13, 192 1) 
Introduction 
Studies on the cereal rusts were made covering various phases of the 
phenomena of rust epidemiology, including the effects of season, age of the 
host plant, etc., on its susceptibility and on the virulence of the disease; 
effects of varying dosage in securing inoculation; effects of the general 
nutritional condition of the host, etc. In carrying out these studies I have 
had the opportunity to convince myself of the frequently observed fact that 
health and vigor of the host favor rather than hinder its inoculation by a 
rust and the further development of the diseased condition. This observa- 
tion has frequently been made and more or less casually reported in the 
literature on the rusts and other fungous diseases of plants. The significance 
of such observations in relation to general theories of immunity and resis- 
tance to disease has, however, nowhere been adequately recognized, and 
I have thought it worth while to bring together the available evidence 
bearing on this point. 
It is a commonplace of pathological theory that the health and vigor of 
an organism and its susceptibility to disease are antithetic variables, that 
as one increases or is increased the other diminishes or is diminished corre- 
spondingly. Adami (1910,^ i: 409), summarizing the subject of predis- 
position to disease, lists the causes of acquired susceptibility as (i) social 
and environmental conditions; (2) injury; (3) malnutrition; (4) previous 
attack of the same disease or other infectious disease; and (5) exhaustion; 
all of them factors diminishing the vitality of the host. Zinnser (1914, 
p. 59), discussing the broader principles of infection and resistance, states: 
A person suffering from functional impairment of any kind is more likely to permit the 
invasion of a pathogenic microorganism than is a perfectly healthy well-nourished indi- 
vidual of the same species. 
Kolmer (1917, p. loi) says, similarly: 
Acquired susceptibility . . . may be due to various factors, most of which lead to a 
state of reduced vitality, normal physiologic processes being impaired to a greater or less 
degree. 
^ The list of literature cited will be found at the conclusion of the second paper of 
this series. 
183 
