XXXIV INTRODUCTORY OBSERVATIONS. 



Various gafes produce an alteration in the ftate 

 of the blood : experiment, it is true, has been 

 chiefly direcled to blood after proceeding from 

 the body of the animal, and the difficulty of the 

 fubjed has hitherto prevented a full confidera- 

 tion of what are the principal phenomena on that 

 which ftill continues to flow- during life. Whe- 

 ther or not the change there produced is fuffi- 

 cient to deflroy the animal, the operation of gafes 

 on the mufcular and nervous fyftem is very con- 

 fpicuous, and efpecially on the former, perhaps, 

 becaufe it may then be more eafily recognifed. 

 Animals, at the fame time, in fome inftances cer- 

 tainly die from abfolute faffocation ; for the ex- 

 cefiive irritation produced by gafes will clofe the 

 entry to the lungs, and death enfue before one 

 infpiration is completed. The general operation 

 is moll probably onmufcular irritability and the 

 nerves, more efpecially when we refied: that the 

 animals refpiring fo very little, as fome are known 

 to do, c^n not efcape the pernicious confequence 

 of refpired air. Yet we mufl admit, that if they 

 refpire at all, which it is mod likely they do, by 

 abforbing air from water, if they are aquatic ani- 

 mals, they will alfo abforb exhalations, and thus 

 be defcroyed. 



Drowning and ftrangling are equally fatal to 

 life as fuffocation in mephitic vapours j but the 



irritabilitv 



