BY DR. BURDON-SANDERSON. 331 



den tightening of the anterior abdominal wall, accompanied by 

 convulsive twitchings of the limbs. The second stage begins 

 by a change in the phenomena quite as marked as when the 

 exclusion of air is complete. Suddenly, the violent expulsive 

 efforts cease, and theinspiratory movements assume the charac- 

 ter already described, consisting in spasmodic contractions of 

 the diaphragm, accompanied by gasping movements of the 

 head and neck, the most marked difference being that the arte- 

 rial pressure, instead of sinking with each inspiratory effort, 

 rises, the rise being accompanied by an equally considerable 

 acceleration (see Fig. 263a'). In the dog this phenomenon is so 

 obvious that it can be judged of quite as well by watching the 

 mercurial column of the manometer as by the tracing. As re- 

 gards the gradual diminution of the frequency of the contrac- 

 tions of the heart during the first part of the period of collapse, 

 and their gradual acceleration as extinction approaches, the 

 phenomena are the same, whatever be the mode in which 

 asphyxia is produced. As regards the final respiratory move- 

 ments, and the stretching convulsions which are associated 

 with them, nothing need be added to the description previously 

 given. 



The preceding facts may be summed up as follows : In the 

 first stage of asphyxia (understanding by the term, that part 

 of the process which culminates in the struggle), the phenomena 

 are of two kinds. At first, we have merely over-activit3 r of the 

 respiratory apparatus (hyperpnoea) ; at the end, expiratory 

 convulsion. The convulsive movements are so distinct from 

 those proper to expiration, that we are compelled to assign 

 their origin to a special centre. This centre is often called the 

 "convulsion centre." It is probably identical with that from 

 which the co-ordinated expiratory movements of dyspnoea (hy- 

 perpncea) spring ; for in asphyxia we see that these last pass 

 into convulsions by insensible gradations. 1 When the struggle 

 with which the first stage closes is succeeded by the calm of 

 the second, all voluntary muscles, excepting those which are 



1 Fig. 263a is taken at the beginning of the second stage of slow 

 asphyxia. Almost every inspiration is immediately followed by two or 

 three cardiac contractions, succeeding each other at very short in- 

 tervals. 



2 It is important to notice that the convulsion of asphyxia is identical 

 with that produced in Kussmaul and Tenner's experiment, both haying 

 the expiratory character. If that experiment is performed in an animal 

 in the state of apnoea, the arrest of the arterial circulation in the intra- 

 cranial nervous centres at once induces respiratory movements ; and if 

 the closure of the arteries continues, the animal passes through the suc- 

 cessive stages of dyspnoea, and finally becomes convulsed just as in as- 

 phyxia. If at this point the arteries are released, the animal relapses 

 gradually, after one or two vigorous inspirations, into the condition of 

 apucea. 



