Respiratory Rhythm in Frogs. 



5i 



cerebrum was then plugged with absorbent cotton and absorbent 

 cotton was placed all round the wound so as to absorb any fluid 

 which might escape from the depression left by the removal of the 

 roof of the skull. With practice the operation could be performed 

 in 3 to 4 minutes, and, if successful, within 3 to 5 minutes after 

 the operation respiration, which at first is suspended, is resumed. 

 After about 5 to 10 minutes, the rhythm of respiration usually 

 becomes constant and, if the frog be left untouched, remains so 

 for over two hours. 



After an interval of 1 5 minutes, to allow all shock effects to 

 subside, drops of various solutions were placed upon the exposed 

 surface of the medulla oblongata and their effect upon the respi- 

 ratory rhythm noted. 



It was found that N/10 solutions of acids (hydrochloric, sul- 

 phuric, lactic, oxalic) caused a notable acceleration. Thus in a 

 frog breathing at the rate of about 19 respirations a minute the 

 application of N/10 H 2 S0 4 quickened the rate, within two minutes, 

 to 50 respirations per minute. In other instances less acceleration 

 was obtained, but in all cases it was very marked, except when the 

 respiratory rhythm before the application of the acid was very 

 convulsive and irregular in character owing to injury of the medulla 

 during the operation ; in these instances it is possible that only the 

 spinal centers were functioning. 



One per cent. KCN caused complete stoppage of respiration 

 within three to five minutes. Strong reducing agents (1 per cent, 

 formaldehyde, M/10 K 2 S, M/10 hydroquinol, 3/4N sulphurous 

 acid) caused marked slowing or stoppage of respiration. Oxidiz- 

 ing agents (20 per cent. Kahlbaum's C. P. H 2 0 2 , N/10 KMn0 4 , 

 N/10 Fe 2 Cl G ) accelerated the rhythm but not markedly. Respi- 

 ration was inhibited by N/10 CuCl 2 and slowed, but not markedly, 

 by N/10 HgCl 2 . Solutions of much higher osmotic pressure than 

 the blood {e. g., pure glycerol) moderately accelerate the rhythm 

 and render it irregular ; prolonged action of solutions of much 

 lower osmotic pressure than the blood (distilled water, tap water) 

 greatly slows the respiratory rhythm and may ultimately suppress 

 it altogether. In confirmation of Maxwell's results I find that 

 sodium oxalate has no effect upon the rhythm. 



It may be questioned whether the effects observed are really 



