[MACLEOD] THE RESPIRATORY CENTRE 87 



remained so, particularly in young animals, even during compression 

 of the vertebral arteries; whilst in other animals apnoea gradually 

 supervened, but could be immediately terminated by allowing some 

 arterial blood to reach the medulla by momentarily releasing the 

 vertebrals. The reflex activities of the decerebrate animal varied 

 considerably according to the exact position of the cut. When this 

 was well forward of the anterior corpora quadrigemina the animals, 

 after the effects of the anaesthetic had passed off, were highly excit- 

 able and behaved as if they felt some pain. Section by a scalpel a 

 little further back immediately removed these mimetic reactions, 

 but the resulting preparation was not as a rule so satisfactory as when 

 the first cut had been in the correct position (i.e. through the anterior 

 corpora quadrigemina). When the cut involved the posterior corpora 

 quadrigemina spontaneous breathing rarely returned except in very 

 young animals, and even in them it was usually irregular and un- 

 satisfactory. In a succeeding paper we shall show that an abundant 

 oxygen supply to the centre could usually be counted on to restore 

 the 'breathing to normal in those cases in which it was irregular and 

 spasmodic. 



The alveolar air was collected by inserting into the trachea 

 (through a side tube in the tracheal cannula) a narrow tube (gum- 

 elastic catheter), the outer end of which was connected with an all- 

 glass graduated syringe (10 cc, but capable of holding about 16 cc.) 

 with the piston well smeared with vaseline. Towards the end of nor- 

 mal respiration the piston was withdrawn taking in from one half 

 to one cubic centimetre. This process was repeated for several suc- 

 ceeding expirations after which the air was expelled again into the 

 trachea so as to wash out the dead space of the tubing. By a repeti- 

 tion of the above procedure a sample of about 10 cc. of alveolar air 

 was then collected for analysis. The analysis was carried out in a 

 10 cc. Haldane gas burette, the accuracy of which had been carefully 

 checked against Brodie's apparatus. 



There can be no doubt that the fractions of air collected towards 

 the end of normal expirations is alveolar air in the usually accepted 

 sense. The average tidal air of a cat is generally about 35 cc. and the 

 dead space from the point of insertion of the catheter to the alveoli 

 cannot be more than 10-12 cc. so that the last few cubic centimetres 

 of air of a normal expiration, from which the fractions of 0-5-1 cc. 

 are collected, must be undiluted alveolar air, even after allowing for 

 the possibility that some of the peripheral layers of air in the trachea 

 do not move so quickly as the axial currents (cf. Henderson, Chilling- 

 worth and Whitney, Am. Journ. Physiol., XXXVIII, p. 1). 



