42 Dr. W. Marcet. The Influence of Exercise [June 8, 



was accessible, were entirely unable to form the green or brown 

 ground-colour. The production of dark superficial cuticular pigment 

 was, however, unchecked. One of the larvro fed in this way was 

 perfectly healthy, and had become nearly mature when it was acci- 

 dentally killed. Many others died early, but resembled that last 

 described in the inability to form a ground-colour. 



The experiment seems to leave no doubt as to the validity of the 

 conclusions previously reached. Interesting questions as to the 

 changes passed through by the derived pigments are suggested by 

 this inquiry. 



Y. " The Influence of Exercise on the Interchange of the 

 Respiratory Gases." By W. MARCET, M.D., F.R.S. Re- 

 ceived May 18, 1893. 



I had the honour of communicating two papers to the Royal 

 Society on the interchange of pulmonary gases one in June, 1891,* 

 and another in June, 1892. t 



The methods adopted and instruments employed have been fully 

 described, and as the present inquiry is a continuation of the former 

 investigation, carried on by similar methods and with the same 

 instruments, there will be no necessity to refer to either of these on 

 the present occasion. 



It might, however, be stated that the expired air was collected in a 

 bell- jar of a capacity of 40 litres, and over salt water ; the C0 2 was 

 determined by Pettenkofer's method, and the O by means of an 

 eudiometer of a special construction. A short historical sketch of 

 the work done on the subject under consideration has been given in 

 the previous papers. 



I have been very ably assisted in the present inquiry by Mr. 

 Bernard F.Davis, B.Sc., who kindly submitted to experiment, and 

 carried out for me, with every care, many determinations of carbonic 

 acid and oxygen. 



The object of the present communication is to show the influence 

 of exercise on the interchange of pulmonary gases, but I must beg 

 leave to preface the subject with a few remarks. 



It has occurred to me that the words " interchange of respiratory 

 gases" might not at first sight carry with them a perfectly clear mean- 

 ing. The word " interchange " obviously refers to the movement of 

 two gases exchanging places, and this applies to the passage of the 

 oxygen of the air into the blood through the substance of the lungs, 



* ' Proceedings Eoy. Soc.,' vol. 50. 

 f ' Proceedings Eoy. Soc.,' vol. 52. 



