CHLOROFORM A POISON 19 



can state that such a percentage may be fatal after the lapse 

 of about two hours. 



The writer has conducted a series of experiments again on 

 the same animals to determine the percentage of chloroform 

 required to abolish the corneal reflex after varying periods of 

 anaesthesia. In these experiments an apparatus designed by 

 the writer for the administration of known percentages of 

 chloroform was used {Transactions of the Royal Medical and 

 Chirnrgical Society, 1905). The method adopted consisted in 

 diminishing the concentration of chloroform administered so 

 long as the corneal reflex did not reappear. The following are 

 the approximate values obtained : 



Percentages of Chloroform in the inspired air required to abolish the corneal 



reflex in cats. 



After i hour ro per cent. 



>j 1 »j • . o*8 



„ 2 hours * .07 



» 3 5 j o'6 



„ 4 » 0-5 



» 5 jj °'4 



These figures show how marked is the diminution of 

 percentage required to abolish this reflex as anaesthesia 

 advances. 1 



We must now turn to the second factor which influences 

 the rate of absorption of chloroform by the blood — namely, 

 the rate of blood stream through the lungs. It is clear that the 

 slower the blood stream the less vapour of chloroform will 

 be absorbed, for there will be a deficiency of supply of fresh 

 blood with a low chloroform vapour pressure. But although 

 less will be absorbed, yet the blood will contain a greater 

 amount of chloroform, since the blood will have a longer 

 exposure to the vapour in the alveolar air. This point appears 

 to the writer to be of extreme importance, for it shows that 

 the beginning of heart failure will cause the blood which 



1 We must not, however, deduct from these figures that a concentration in 

 the lymph corresponding to a 0*4 per cent, vapour is sufficient to abolish the 

 corneal reflex after five hours purely by virtue of its anaesthetic properties, for 

 the recent researches of Sutherland Simpson and Herring have shown that the 

 diminution of temperature following prolonged administration of anaesthetics is 

 in itself narcotic (Journal of Physiology, vol. xxxii. p. 305). 



