[Annals N. Y. Acad. Sci., Vol. XXIII, pp. 1-75. 14 May, 1913] 



A PHYSIOLOGICAL STUDY OF THE CHANGES IN MUSTELUS 

 CANIS PEODUCED BY MODIFICATIONS IN THE 

 MOLECULAE CONCENTEATION OF THE 

 EXTEENAL MEDIUM^ 



By G. G. Scott 



(Presented hy title lefore the Academy, 10 March, 1913) 



CONTENTS 



Page 



Introduction 2 



Historical sketch 5 



Normal osmotic pressure of the blood of Mustelus 6 



Changes in the osmotic pressure of the blood due to alterations in the 



concentration of the external medium 8 



Preliminary study 8 



Changes from the normal condition until death in fresh water and 



concentrated sea-water 11 



Reverse changes brought about by a return to sea-water after immer- 

 sion of the organism in fresh water and concentrated sea-water .... 22 



Role of the gills in the osmotic changes of the blood 25 



Osmotic pressure of the blood of an elasmobranch taken from brackish 



water 30 



Effect of loss of blood on the osmotic pressure of the blood 34 



Additional changes in the blood due to alterations in the concentration of 



the external medium 36 



Changes in the erythrocytes 36 



Changes in the specific gravity of the blood 44 



Changes in the percentage composition of the water and the solids of 



the blood 44 



Changes in the nitrogen content of the blood 46 



Changes in the urea of the blood 47 



Changes in the salt of the blood 48 



Regulation of the osmotic pressure of the blood 51 



Presence of salts in the external medium after immersion of Mustelus in 



fresh water 54 



Effects of changes in the osmotic pressure of the blood on blood pressure, 



respiration and cardiac activity 55 



Discussion 63 



Conclusions 71 



Bibliography 73 



1 Submitted in partial fulfilment of the requirements for the Degree of Doctor of 

 Philosophy, in the faculty of Pure Science, Columbia University, 



