CAUSES OF QUICK EESPIRATION. 329 



^farcy's levers ; and as each respiratory movement draws the 

 ends of the cylinders wider apart, or allows them to approach, 

 the air is rarefied or compressed, and a corresponding movement 

 is transmitted to the lever. Bert has modified this, and made 

 it more sensitive by making the cylinder itself of metal, and 

 its ends of india-rnbber. Another method — one more ordinarily 

 employed — is to introduce one limb of a T-tnbe into the 

 nostril or trachea of an animal, or to connect it with a tracheal 

 cannula. The respired air passes through the other end, and 

 the third limb is connected with one of Marey's levers. 



Is Quickening of Respiration due to Irritation of the Var/i? — 

 When the respiratory movements become quickened by the 

 injection of a drug into the circulation, the first cause to which 

 it may be due, mentioned in the preceding table, is irritation of 

 the ends of the vagus in the lung. In order to discover 

 whether this be the cause or not, the vagi must first be divided 

 and the drug injected. If it acts only on the ends of the vagus, 

 the respiration which was quickened by injection when the 

 vagi were intact, will not be quickened by it when these nerves 

 jire divided. 



Is the Quiehening due to E.ccitement of the Voluntarif Nervous 

 Centres ? — Tliis cause of quickening is eliminated by narcotis- 

 ing the animal with opium or chloral, or by removing the 

 cerebrum. Tor the method of doing this, see Sanderson, 

 Handhooh for the Phijsiological laboratory, p. 295. 



Is it due to Increased Temperature .? — If the temperature of 

 the animal has risen above the normal — the fact can readily 

 be ascertained by the thermometer — it may then be reduced 

 by the application of cold water or ice, or by a stream of cold 

 air directed on the surface of the skin. Unless the cooling be 

 effected very gradually, these applications cause reflex disturb- 

 ance of the respiratory movements through the cutaneous 

 nerves. 



Is it due to Increased Venosity of the Blood ? — The drug may 

 produce this by its action on the blood ; and this is to be deter- 

 mined by the means already described. Generally we let a little 

 blood issue from an artery ; and if its colour be of normal bright- 

 ness, we conclude that the gases it contains are also normal. 



