54 North Carolina Experiment Station 
of the heat regulating mechanism. This condition follows the entrance into 
the body of pathogenic bacteria and their toxic substances. Accompanying 
this condition is thirst, weakness, and alteration in body secretions. The 
fever may begin abruptly with a chill, or it may be intermittent. Hirsch, 
Muller, and Roily (1) have advanced the view that fever results in conse¬ 
quence of a derangement of metabolic condition of tissue cells by poisonous 
substances. This theory is well adapted to those febrile conditions following 
the entrance of pathogenic bacteria into the system, and also admits of the 
possibility that there are heat regulating centers in the brain which may be 
upset by the toxemia produced by infection. In the temperature studies in 
this investigation the temperatures of infected birds ranged from normal to 
113 degrees F. 
Heat is dissipated from the body of the bird, to a limited extent, by the 
skin through the process of radiation and convection, though the feather 
coat retards this process, and to a greater extent by the way of the pulmonary 
passage, the heat being transferred to the inspired air. The respired air is 
made to oscillate back and forth across the moistened mucous surface, and 
some bound heat is also eliminated by the droppings. Hence, respiration is 
increased when excess of heat is present in the body. The normal physiolog¬ 
ical respiratory centers in the brain govern both the length and depth of 
breathing (1), thus determining lung ventilation. In Figure 20 there is 
shown a kymographic tracing of the respiratory movements in an artificially 
infected case of avian typhoid. It is noted that in the preinoculation study, 
the hen breathed 19 times in 23 seconds and that in the initial stages of the 
disease the response is a greater depth in the respiratory movement (20 in 
23 seconds) which constitutes labored breathing. In the later stages the 
breathing is again more shallow and accelerated, amounting to 27 respiratory 
movements in 23 seconds. In many instances there is a serous effusion into 
the lung alveoli which further complicates the process of heat dissipation. 
The pre-inoculation respiration in the figure shown is above normal, but the 
three readings are comparable as the tracing was taken under the same con¬ 
ditions, except for disease advancement. Great care is always exercised to 
avoid exciting the fowl, as under the strain of excitement and fear the respi¬ 
rations are sure to be increased. 
The increase in respiration, as the result of disease, is due to a stimulation 
of the heat dissipating center. The normal respirations, as determined for 
utility cocks, as Rhode Island Reds and Plymouth Rocks, is 20 times per 
minute, and for hens of similar breeds, 36 times a minute (14). In the arti¬ 
ficial infections studied the respiration was irregular in frequency, being 
recorded in one instance as high as 63 per minute. 
