334 ESCH AND HAZEN 



which could be induced as a consequence of long-term stressor input. 

 It is also known that some corticosteroids cause significant changes 

 in carbohydrate metabolism and suppress inflammatory reactions. 

 According to Selye, these responses collectively provide protection 

 against the stressor. We should note, however, that the action of 

 corticosteroids in suppressing inflammation may actually be counter- 

 productive since the organism simultaneously becomes more vulner- 

 able to infection by pathogenic organisms. A significant body of 

 literature exists which details the impact of increased corticosteroid 

 output in terms of reducing both natural and acquired resistance (for 

 details of the relationship between stress and parasitism, see Esch, 

 Gibbons, and Bourque, 1975). 



The third stage of the GAS, exhaustion, occurs when, after long 

 and persistent stressor input, the cells of the adrenal cortex become 

 exhausted. At this time there is functional and structural deteriora- 

 tion of the cortical cells, resulting in cessation of corticosteroid 

 production. If this occurs, death of the stressed organism rapidly 

 follows. 



Thus, if stressor input continues over a long period of time or if 

 it is of sufficient magnitude, there is a potential for mortality either 

 from exhaustion of the adrenals or from side effects such as stroke, 

 hypertension, bleeding ulcers, arthritis, and infection with patho- 

 genic agents. We should emphasize that, although the concept of 

 stress is accepted by most biomedical scientists, there is discussion 

 about whether stress is necessarily related to some of the diseases 

 mentioned. 



Definitions of Stress 



Stress as a process can be more or less adequately described at 

 the individual level, but most definitions of stress appear to be less 

 than acceptable. This is especially true since most of the definitions 

 were developed to apply only at the individual level and only for 

 animals. We know, however, that the stress concept can be extended 

 to plants (Harper, 1967; Vadas et al., 1976) and to the population 

 (George, 1977) and ecosystem (Cairns, 1976) levels of organization. 



Let us consider, for example, the definition of stress offered by 

 Selye (1956): the "sum of all physiological responses by which an 

 animal attempts to maintain or re-establish a normal metabolism in 

 the face of a chemical or physical force." In some ways this 

 definition is acceptable, but we feel it is too restrictive because it 

 excludes plants and it is not applicable at the ecosystem level. 

 Homeostatic processes operating at the individual level and forces 

 that tend to maintain stability or equilibrium at the ecosystem level 



