258 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



2 drachms of liquor morphise, which is equal to 1 grain or 

 5 centigrams of morphia. This dose is for injection into a 

 vein: when injected subcutaneously, rather more should be 

 given. If the dog be above or below middle size, the dose must 

 be proportionately increased or diminished. We must be care- 

 ful not to give too much opium to old dogs, or they will die. 

 Opium is preferred by some to morphia, as producing more 

 certain narcosis, and being less likely to produce the excitement 

 and hypera3sthesia which sometimes follow the administration 

 of morphia. 



When we wish to render the animal absolutely motionless, or 

 to observe what effect any drug will produce after the motor 

 nerves have been paralysed, we give curare. Small doses of 

 this remarkable substance paralyse the motor nerves of muscles, 

 but leave the vagi and vaso-motor nerves unaffected. Large 

 doses of it seem also to cause paralysis of the vagi. It affects 

 the blood-pressure to a certain extent, moderate doses contract- 

 ing the vessels and raising the pressure, while large ones lower 

 it. The dose of curare for a frog is about 1 to 5 drops or more 

 of a solution of 1 part in 1000. The dose varies with the size 

 of the frog and the purpose for which we wish it. If we wish 

 to observe the circulation microscopically, we must not give too 

 large a dose, or the heart may stop. To rabbits, -J to 1 c.c. or 8 

 to 15 minims, and to dogs, 4 to 6 c.c. or 1 to 2 drachms, of such 

 a solution, may be given.* 



Definite rules cannot be laid down as to the experiments in 

 which narcotics may or may not be used. The experimenter 

 himself must judge in each case whether their action is likely 

 to disturb that of the drug to be experimented on or not. For 

 this purpose, he must know the action which the narcotics them- 

 selves produce ; and I will, therefore, mention in a few words 

 what that of each is. 



Action of Narcotics. — Chloral acts on the brain, producing 

 deep sleep, during which there is no sensation or voluntary 

 motion. The reflex function of the spinal cord is first increased 

 and then diminished in frogs ; in guinea-pigs and rabbits, it is 



* Curare may be obtained from Messrs, Hopkin and Williams, New Cayen- 

 disli Street, London ; or from Bruckner and Lampe, Leipzig. 



