Royal Ltstiiutiofi of Great Britain. 73 



experimental investigation into the ratio which obtains between the 

 quantity of the respiration and the degree of the irritability in the 

 different series and forms of being in the animal kingdom. 



The quantity of the respiration is expressed by the quantity of 

 oxygen removed in a given space of time. 



The degree of the irritability is denoted by the degree and dura- 

 tion of the contraction of the heart and of other muscular parts, on 

 the application of a given degree of stimulus. 



These two properties are always found to be in an inverse ratio 

 to each other. In animals of a high respiration, as the birds and the 

 mammalia, the degree of irritability is low ; in animals of a low re- 

 spiration, as the tortoises, the serpents, the batrachia, the degree of 

 initability is extreme. 



It is absolutely necessary to distinguish activity from irritability. 

 The former seems to depend upon the action of a highly arterial 

 blood upon the nervous system, and is great in birds and the mam- 

 malia; the latter is inherent in the muscular fibre itself, and seems 

 to result from its peculiar organization and condition at the time. 



The law of inverse respiration and irritability applies not only to 

 the different individuals of the animal series, but to the different 

 forms of the same animal. The egg, the tadpole, the larva, have 

 respectively a lower respiration and a higher irritability than the 

 same beings in their subsequent higher states of existence. 



The same law still obtains in animals which undergo a change of 

 condition from the operation of some natural causes, as in the diyr- 

 iiation and hibernation of the bat ; in torpor from cold in animals 

 which do, or do not, hibernate; in the case of the privation of food, &c. 



But the most extraordinary exemplification of this law is in the 

 double heart of birds and of the mammalia itself. The left side of 

 this organ, which receives a highly arterialized or respired blood, 

 possesses a low degree of irritability ; the right side, which receives 

 blood of an unrespired character, possesses a high irritability : the 

 latter continues to beat after the former has ceased its contractions. 



Various deductions were drawn from these observations. It was 

 shown, that with the high respiration and low irritability coincide, 

 1. great necessity for air and food; 2. a high animal temperature ; 3. 

 great activity; 4. little tenacity of life; and, 5. a greater power of 

 bearing augmented than diminished stimulus in general :-^And that 

 with a high irritability and a low respiration co-exist, 1. the power of 

 sustaining the privation of air, of food, &c.; 2. alow animal tempe- 

 rature ; 3. little activity ; 4. great tenacity of life ; and, 5. little power 

 of bearing the action of augmented stimulus. The former class are 

 more injured by exposure to cold, the latter by heat. 



The lecture was concluded by a hasty reference to the interesting 

 facts detailed by Legallois and by Mr. Edwards, which, although 

 given in an isolated form by those authors, admit of being readily 

 explained and arranged by a reference to the law, — that the quantity 

 of the respiration is inversely as the degree of the irritability, and 

 to the corollaries whirh flow from it. 



'rhird Series. Vol. 1. No. \,Juhj 1832. L 



