830 RESPIRATION. 



lity, which contrasts in the most striking way with the storm 

 which preceded it. The condition of the circulation at this 

 stage can be best judged of by the tracing, Fig. 2636.' Inspi- 

 rations occur at long but tolerably regular intervals, and each 

 iuspiratory act is accompanied, not, as in normal inspiration, 

 by an increase of arterial pressure, but by a marked diminu- 

 tion. The mean arterial pressure, which at the beginning of 

 the second minute is far above the normal, sinks considerably 

 below it towards the end. Third and .fourth minutes. As 

 death approaches, the thoracic and abdominal movements, 

 which are entirely inspiratory, become slower and slower as 

 well as shallower. The diminution of frequency is, however, 

 never uniform, the inspirations occurring, for the most part, 

 in successions of two or three efforts, with long pauses between 

 them. In each act the accessory muscles of inspiration co- 

 operate with the diaphragm in the production of the result, 

 and towards the close other muscles come into spasmodic 

 action which are not usually regarded as inspiratory muscles 

 at all, although, in all probability, they act by virtue of motor 

 impulses originating in the inspirator}' centre. In these 

 spasms, which accompany the final gasps of an asphyxiated 

 animal, the head is thrown back, the trunk straightened or 

 arched backwards, and the limbs are extended, while the mouth 

 gapes and the nostrils dilate. They are called by physiologists 

 stretching convulsions, and must be carefully distinguished 

 by the student from the expiratory convulsions previously 

 described. 



110. Asphyxia by Slow Suffocation. When an animal 

 is allowed to breathe the same quantity of air repeatedly 

 and continuously out of a bag, the process being of much 

 longer duration, the phenomena can be studied with greater 

 facility. As, however, its duration depends on two variable 

 conditions, viz., the respiratory capacity of the animal and the 

 capacity of the receptacle from which it breathes, it is not pos- 

 sible to describe the phenomena with reference to periods of 

 fixed duration. It is sufficient to divide the process into two 

 stages, the limits of which will be readily understood from the 

 preceding paragraph. The first may be called that of hyper- 

 pnoca. The respiratory movements, at first natural, are gradu- 

 ally exaggerated, both as regards their extent and frequency, 

 while the arterial pressure rises. Towards the end of the 

 period, as in the former case, the expiratory movements gain 

 in vigor, both absolutely and relatively to those of inspiration, 

 so that each inspiratory act is immediately followed by a sucl- 



1 Fig. 2636 is taken toward the end of the second minute of asphyxia 

 by occlusion. The mean arterial pressure is gradually sinking; each in- 

 spiration is accompanied by a depression of arterial pressure. 



