BY DR. BURDON-SANDERSON. 329 



nous muscles and external intercostals, are the most important, 

 as indicating successive stages. For a comprehensive study 

 of dyspnoea, as it affects not merely the respiratory movements, 

 but the circulation and the functions of the nervous system, 

 those experiments are best in which the disorder can be watched 

 from its beginnings in mere increase of functional activity (hy- 

 perpncea), to its issue in asphyxia or suffocation. These may 

 consist, either in complete obstruction of the air-passages, in 

 which case death occurs very rapidly (in 4-5 minutes in the 

 dog, a shorter time in the rabbit), in allowing the animal to 

 breathe out of a bag with which its respiratory cavit}^ is in 

 air-tight communication, or from a gasometer (the instrument 

 represented in Fig. 251), into which definite mixtures of gases 

 can be continuously introduced. 



109. Asphyxia by Complete Occlusion of the Tra- 

 chea. For this purpose, a canula must be fixed air-tight in 

 the trachea, the mouth of which is of such form that it can be 

 plugged with a cork. If it is desired to obtain a tracing of the 

 variations of tension which the air so inclosed in the respira- 

 tory cavity undergoes, the cork must be perforated and fitted 

 with a tube which communicates with a mercurial manometer, 

 the movements of which are recorded on the cylinder of the 

 Irvmograph, simultaneously with the variations of pressure 

 in the crural artery. The tube must be of small bore and have 

 thick walls. The phenomena, as they present themselves in 

 the dog, may be enumerated as follows : First minute. Ex- 

 cessive respiratory movements, in which at first the expansive 

 efforts of the thoracic muscles, afterwards the expulsive efforts 

 of the muscles of the abdominal wail, are most violent. During 

 this period the arterial pressure increases, but it is extremely 

 difficult to measure it, on account of the modifying influence 

 of the thoracic movements. Towards the close of the first 

 minute the animal becomes convulsed. These convulsions must 

 be attentively studied, because they are the type, by compari- 

 son with which all other convulsions of the same order are de- 

 scribed or defined. The prominent fact with respect to these 

 convulsions is that they are expiratory. At first, indeed, they 

 seem to be nothing more than exaggerations of the previous 

 expulsive efforts. Afterwards, the contractions of the proper 

 expiratory muscles are accompanied by more or less irregular 

 spasms of the muscles of the limbs, particularly of the flexors. 

 Second minute. Early in the second minute the convulsions 

 cease, often suddenly; simultaneously with their cessation, the 

 expiratory efforts become indistinguishable. The iris is now 

 dilated to a rim ; the eye does not close when the cornea is 

 touched, nor does the pupil react to light ; all reflex reaction 

 to stimuli has ceased. All the muscles, except those of inspi- 

 ration, are flaccid, and the animal lies in a state of tranquil- 



