364* INFECTION AND RESISTANCE 



weakness. The animals fall to the side, the legs and trunk muscles 

 twitch irregularly, and the respiration becomes slow and shallow; 

 the thorax never entirely contracts, but remains in a more or less 

 expanded condition. The very evident dyspnea is of an inspiratory 

 character. The excursions of the lung itself seem to grow shallower 

 and shallower in spite of apparent strong inspiratory efforts the 

 volume of the thorax and lung remaining in the expanded condition. 

 At this stage evidences of motor irritation may appear, in that the 

 animal may arise and attempt to run. More often, however, in this 

 phase general convulsions set in, often several times repeated, and 

 in these the animals usually die. 



On the other hand, after cessation of convulsions they may lie 

 perfectly still on the side as though paralyzed, the breathing becom- 

 ing gradually slower and more shallow, finally ceasing entirely. The 

 heart may continue to beat for a considerable time after the breath- 

 ing has stopped. 



If such an animal is immediately autopsied a very characteristic 

 condition is found to which, in the essentials, attention was first 

 called by Gay and Southard. 12 They speak of finding "pulmonary 

 emphysema as a constant feature at autopsy," and attribute the 

 anaphylactic death in guinea pigs to cessation of respiration in the 

 inspiratory phase under the influence of respiratory central intoxi- 

 cation. 



The lungs of such guinea pigs after death are found distended 

 and completely filling the thorax. They are usually pale and blood- 

 less and do not collapse as the pleurae are opened. On microscopic 

 examination the alveoli are seen to be distended and small hemor- 

 rhages may appear upon the serous surfaces. According to Gay 

 and Southard, furthermore, histological study of the other organs 

 shows also hemorrhages in the brain, stomach, heart, cecum, and 

 spleen more rarely in other organs, and there are local fatty 

 changes in the capillary endothelium which they regard as causa- 

 tively related to the hemorrhages. 



That the respiratory symptoms are the most striking feature of 

 the clinical picture of guinea pig anaphylaxis had, as a matter of 

 fact, been noticed by Ivosenau and Anderson. A detailed physiologi- 

 cal study of the mechanism of the respiratory death in these cases 

 was first made, however, by Auer and Lewis 13 in 1909. 



These investigators showed that, during the later respiratory 

 symptoms, little or no air enters the lungs, although the animal 

 makes violent respiratory efforts. This is due, as they found, to a 

 tetanic contraction of the small bronchioles, which practically oc- 



12 Gay and Southard. Jour. Med. Res.. Vol. 16, 1907; Vols. 18 and 19, 

 1908. 



13 Auer and Lewis. Jour, of the A. M. A., Vol. 53, p. 458, 1909; Jour, 

 Exp. Med., Vol. 12, 1910. 



