METHOD OF EXPERIMENTATION. 175 



meter connected with the carotid of a rabbit falling, when the 

 vapour of the nitrite was inhaled. Pievious division of the 

 depressor nerves did not affect the rcoult. 



The diminished blood-pressure which it produces, led me to 

 apply it in angina pectoris, and the good results I obtained 

 made me anxious to investigate more closely the nature of its 

 sictiun. An excellent opportunity for doing so was afforded me 

 by the kindness of Professor Ludwig, in whose laboratory at 

 Leipzig the experiments, the result of which I am about to 

 give, were carried on. With the exception of one or two on 

 dogs, they were made upon rabbits ; and instead of allowing the 

 animals simply to inhale the vapour, artificial respiration was 

 employed, the apparatus being so arranged that the air could be 

 either sent direct from the bellows, through a tube in the 

 trachea, to the lungs, or passed through a vessel containing the 

 vapour of the nitrite. The advantages of this arrangement 

 were that the bellows being worked by an engine with great 

 regularity, the disturbing intiuences of unequal respiration on 

 the blood-pressure were to a great extent avoided. One of the 

 chief of these is that any strongly smelling vapour, and nitrite 

 of amyl among others, acting on the nose of rabbits, causes 

 suspension of the respiration for a short time ; and the alteration 

 in the condition of the blood thus produced causes irritation of 

 the vagus and slowing of the heart's action; such as Drs. 

 Eutherford and Gamgee found accompanying the sinking of the 

 blood-pressure in rabbits. 



When air charged with the vapour was passed directly into 

 the trachea of a rabbit the blood-pressure almost immediately 

 sank very much, but the pulse-rate remained nearly unchanged. 

 As the pressure sank general convulsions took plac^ and the 

 pressure immediately rose, notwithstanding the continued 

 inhalation of the vapour, the pulse curves becoming at the same 

 time indistinct, so that the rate could not be well ascertained. 



When the vapour was discontinued after twenty seconds 

 the pressure rose still more quickly, and in a minute at most 

 attained its normal height, as is seen in Fig. 107, where the 

 distance along the abscissa indicates the time, and the ordinate 

 the pressure in millimetres of mercury. This shows that very 



