PHYSIOLOGY OF THE INVERTEBRATA. 175 



Dr. MacMunn uses in his researches three spectroscopes — 

 (i) a microspectroscope, (2) a Hilgers's " Student's Kensing- 

 ton Spectroscope," and (3) a large spectroscope with one 

 dense Hint-glass prism, which is replaceable by a reflection 

 diffraction grating. He has curves adapted to each, so that 

 he can easily correct any error of observation by comparison. 



" The wave-length record of bands has raised the chroma- 

 tology of plants and animals from a state of chaos to one 

 which is daily assuming shape and symmetry, and we are 

 now beginning to perceive relationships and the shadows of 

 generalisations which when made will undoubtedly be of 

 great help to biology." 



From the above remarks it will be seen that the spectro- 

 scope is an instrument of the greatest value not only to the 

 chemist and physicist, but also to the biologist and physiolo- 

 gist. " Until the spectroscope was applied to physiology no 

 one knew what the true colouring matter of the blood was, 

 and the chaotic state of medical knowledge with regard to 

 the cause of the colour of the various animal secretions 

 (of which survivals are still found in many text-books) is 

 sufficiently proved by a perusal of the older text-books, in 

 which one finds the pretended knowledge of the authors 

 cloaked under the adoption of meaningless names, which 

 may have, at the time they were written, brought conviction 

 home to those incapable of judging for themselves, but which 

 show us now what physiological chemistry alone could 

 do, unaided by spectroscopic analysis, in detecting animal 

 pigments and enabling us to follow their metabolism " 

 (MacMunn). 



The Gases of the Blood. 



Very little is known concerning the composition and nature 

 of the gases in the blood of the Invcdcbrcda. 



The author* has ascertained the approximate composition 



* A paper read before the Royal Sociaty of Edinburgh on June 1, 1891; 

 and also in Revue Ginercde des Sciences j)ures et apjdique^s, 1891, p. 395. 



