392 Dr. J. Burdon Sanderson — Croonian Lecture. [Marcli 7, 



which rests on the surface of the mercury in the wide arm of the dynamo- 

 meter, the lower wdth the upper surface of the caoutchouc bag. At their 

 extremities they carry fine sable brushes, by which their movements are 

 inscribed on a roll of paper, to which a horizontal movement is communi- 

 cated by clockwork. By a mechanical arrangement, which need not be here 

 described, synchronical points can from time to time be marked in the two 

 tracings inscribed simultaneously on the paper by the momentary with- 

 drawal of both brushes. The experiments were of the following nature, 

 dogs being employed throughout. 



1. Experiments as to normal respiration. — In these experiments (eleven 

 in number) the dynamometer was connected with the femoral artery, while 

 the breathing-tube v;as connected with the respiratory cavity, either by 

 the trachea, or by means of a mask fixed over the snout. The principal 

 results were as follows 



Exjperiment \ . — Respirations per minute, 9; pulsations, 108. Mean 

 arterial pressure 6*2 inches. The tracings show that each respiratory act is 

 divisible into two parts ; two-fifths being occupied by thoracic movements, 

 the remainder by the pause. Of the former, two-thirds correspond to in- 

 spiration, one-third to expiration. During the pause the arterial pressure 

 gradually sinks, the commencement of inspiration being immediately fol- 

 lowed by an increase of pressure, which becomes still more marked during 

 expiration, but again subsides at its completion. The interval between 

 each two succeeding contractions of the heart is seen to be three times as 

 great in those pulsations which immediately yb//oiy expiration as in those 

 which precede it. 



The other experiments of the series were of a similar nature. In some 

 the relative length of the respiratory intervals and the regularity of the pul- 

 sations rendered it more easy to judge of the precise relation between the tv/o 

 tracings than in others, but in all the results were in complete accordance with 

 those above stated. Even when the frequency of breathing was such that 

 three pulsations corresponded to one respiration (experiment 4), it was ob- 

 served that the diastolic interval which immediately followed expiration was 

 twice as long as either of the other two. In one case the respiratory tra- 

 cing showed that the mode of breathing was peculiar : inspiration was sepa- 

 rated from expiration by a pause of considerable duration, during which 

 the arterial pressure declined and the pulse was retarded. 



2. Ex'periments for the jiurjiose of determining whether the resistance 

 afforded by the T-tiihe to the passage of air in and out of the chest exer- 

 cise any modifying influence on the results. — It was obvious that this end 

 could be best attained by observing the effect of increasing the resistance ; 

 for by so doing, any modifying influence exercised by it would become more 

 obvious. With this vievv^ a series of observations were made on the same 

 animal (under the influence of morphia), in which the resistance was gra- 

 dually increased by inserting plugs of various sizes into the aperture of the 

 T-tube. The tracings showed that even when the aperture was so diminished 



