A. Respiratory center
The location of respiratory centers has been intensively studied, unity of opinions being, however, yet beyond our reach. I am of the opinion that the centers of normal breathings which have rhythmicity are located at the level of striae acoustics and bilaterally in small cell groups situated in the lateral reticular formation (Fig. 1). The evidences are as follows: (a) Careful removal of the part of the pons situated just rostral to the region mentioned above does not affect the pattern of the breathings, except for transtory changes (Fig. 1 and 2). Injury of the region brings about the irregularities of breathings, and the abnormal pattern of breathings, that is, the gasps appear when finally the region is entirely removed (Fig. 1 and 2). (b) Electrical coagulation of the lateral reticular formation at the level of acoustic striae produces the standstill of the normal breathings, being followed sooner or later by gasps, which apparently differ from the normal breathings in that they consist of abrupt and convulsive contractions of the respiratory muscles. We believe that the second center exists to produce the gasps, being mainly localized in the medullary lateral reticular formation which extends from the lower limb of the acoustic striae to the apex. In addition, we want to emphasize that it may be unnecessary to assume the so-called pneumotaxic center to exist in the upper pons.
The pathways of axons coming from the normal respiratory centers descend through the lateral reticular formation of the medulla oblongata to reach the respiratory motoneurons located in the spinal anterior horns via the spinal reticular formation; some fibers may on their way cross on the other side.
By means of unipolar microelectrode the action potentials with a respiratory rhythm can be detected from the normal respiratory centers and centrifugal respiratory pathways (Fig. 3). The inspiratory and expiratory neurons do not show any localized arrangement in the center; they are intermingled with each other, the former being much higher in the degree of activity and greater in frequency of detection than the latter.
As regards the mechanism of the alternation of the activity of the inspiratory and expiratory neurons, some suggestions may be postulated. In the animal whose normal respiratory centers are removed, gasps appear at long intervals. Electromyograms of the respiratory muscles reveal that during the long pauses the expiratory neurons persistently discharge and that these expiratory impulses disappear every time when inspiratory neurons discharge abrupt and short-lasting impulses. As soon as the inspiratory neurons stop discharging, the expiratory impulses reappear with frequency higher than before, decreasing rapidly in frequency. The inspiratory neurons may take the initiative to produce a burst of impulses, which at the same time inhibits transitorily the action of the expiratory neurons that are persistently discharged. In the normal breathing the pause is too short to present a clear picture as observed in the gasping. It seems that the underlying mechanism of the alternation is essentially the same in both cases.
The normal respiratory centers are endowed with the ability to produce impulses spontaneously, and the gasping centers are also able to discharge impulses, although the ability is inferior to the former. However, the spinal cord shows no sign of automaticity at least in the adult animal.
B. The Nervous Regulation of Respiration
(a) In the nondecerebrated animal stimulation of any sensory nerves generally produces the excessive hyperpnea; The inspiratory muscles contract irregularly and powerfully; an inhibitory effect may be only transitorily seen (Fig. 6). Such a hyperpnea as mentioned above can not be produced when the brain, including the inferior colliculi, is removed. This fact suggests that the centers are located in some part of the brain situated rostrally to the inferior col
