720 NATURAL SCIENCE. '^?^" 



this respiratory centre Hence, by some physiologists breathlessness has been 

 attributed to an undue proportion or excess of carbonic acid in the blood. To explain 

 the phenomena of Second Wind, soine writers have alleged that the respiratory 

 centre can become accustomed to the increased amount of carbonic acid present — a 

 condition which has been obser\ed in many human diseases. 



As regards deep-sea fishing, rushing the animal upwards and making the fish 

 thus breathless, is due partly to fright, but still more to altered "atmospheric " and 

 a<iuatic pressures, which cause the contained gases, including the carbonic acid, 

 within the fish to expand and escape in increasing proportions. Evidently the 

 nearer the hooked and suddenly-raised fish is drawn to the surface, the less is the 

 amount of carbonic acid included within the animal's blood ; its breathlessness is 

 nevertheless augmented, thus clearly illustrating that extreme breathlessness may 

 exist with a diminished and diminishing supply of carbonic acid. This fact seems 

 to suggest that some cases of breathlessness may be explained on other grounds than 

 those due to a supposed excess of carbonic acid in the blood. 



I am anxious to learn whether domesticated and wild animals, especially those 

 which are chased or hunted, have been observed to suffer from phenomena 

 similar to those experienced in the so-styled second wind of man, which appears to 

 be analogous to the so-called "blowing" of horses and hounds. 



J. Lawrence Hamilton, M.R.C.S. 



TO CORRESPONDENTS. 



All communications foy the Editor to be addyessed to the Editorial 

 Offices, 67-69 Chancery Lane, London, W.C. 



M. SucHETET {Bi'tuulc, near Godcyville, Seine-lnjiricuyc, Fnincc) is studying the 

 facts and principles of hybridisation, and invites the co-operation of ngituralists 

 who can favour him with observations. 



W. James (Liverpool). — The feathers of Dinornis were firsts described by VV. S. 

 Dallas, Proc. Zool. Soc, 1865, p. 265, and Ann. Miig. Nat. Hist., vol. xvi. (1865), 

 p. 66. 



J. L. R. (Northampton). — The references are unnecessary. Professor Cope's 

 views on Evolution are summarised in his work " The Origin of the Fittest," pub- 

 lished by Appleton, 1887- 



