146 MATERIA MEDIC A AND THERAPEUTICS. 



c. Third stage. Beyond the second stage or degree, chloro- 

 form anaesthesia is highly dangerous, the further action of the 

 drug being attended by complete loss of all reflex excitability 

 of the cord and medulla. The sphincters relax, the pupils 

 are widely dilated and fixed, the globes prominent. The 

 respiratory centre is no longer irritable, and the movements of 

 the chest become weaker, irregular, sighing, and finally cease. 

 The cardiac centre fails, the heart beating irregularly and 

 feebly, and at last stopping in diastole, both from central and 

 from, direct nervo-muscular depression. The blood-vessels 

 dilate, the pressure falls to zero, and the circulation has come 

 to a standstill. It is obvious that the direct effects of chloro- 

 form on the respiratory centre are complicated towards the last 

 by venosity of the blood. Death may occur through the heart, 

 the respiration, or both together. 



2. Analysis of the phenomena of chloroform anaesthesia. 

 Chloroform anaesthesia affords us an excellent opportunity of 

 studying the action of a drug upon the various centres of the 

 nervous system, from the highest downwards. The first parts 

 to be stimulated are the cerebral centres with mental functions, 

 the control of the special senses and consciousness; and these 

 are the first to be depressed and finally annulled. The lower 

 cerebral and spinal centres are affected less and somewhat later, 

 so that a certain degree of excitement of these accompanies the 

 first cerebral depression ; and the spinal centres being no longer 

 controlled by the cerebral, irregular excessive movements of 

 the limbs ensue. As the depression deepens in the spinal 

 centres, the muscles are paralysed. Lastly, the lowest centres 

 of all, those of organic life, connected with the heart, vessels, 

 respiratory organs, and sphincters, situated in the medulla and 

 cord, yield to the action of chloroform. Although affected from 

 the first, it is not until the higher parts have become com- 

 pletely overpowered that the functions of these vital centres are 

 seriously impaired, and death threatens. It is on account of 

 the safe order of invasion of the different centres by chloroform 

 that it has been selected as the proper agent for temporarily 

 arresting consciousness ; we shall find that many other power- 

 ful drugs equally depress the nervous system, but in a direc- 

 tion exactly the reverse. 



The peripheral nerves are affected last of all in general 

 anaesthesia, and it must be repeated that the loss of sensibility 

 to the knife is due to a central, not a peripheral effect. 



The muscles are finally affected directly, as well as through 

 the nervous system. The pupil is dilated in the first stage, 

 probably by stimulation of the sympathetic ; and contracted in 

 the second, and dilated in the third stage, by stimulation and 



