A STUDY OF THE BLOOD OF CERTAIN COLEOPTEEA. 153 



uucliacged). Since the blood darkened on exposure to air, 

 or rather to oxygen, it follows that it contained exceedingly 

 little dissolved oxygen in the straw-yellow condition which it 

 exhibited in the living body. On spectroscopic examination 

 of a layer six millimetres thick the portion of the spectrum 

 lying to the blue end of the green was completely cut off and 

 the green itself in part absorbed, but the red of the spectrum 

 was little altered. "When the blood had become darkened 

 the spectrum became dim but no absorption bands were seen. 

 The brownish-black colour which the blood assumed on ex- 

 posure to air could not be removed by adding ammonium 

 sulphide. 



Odour. — The blood, immediately after collection had a 

 sweet smell somewhat resembling malt extract, but was also 

 distinctly offensive. A faint odour of free ammonia was 

 recognisable. On adding sodium hydrate and boiling, the 

 issuing vapour readily turned neutral litmus paper blue, thus 

 affording additional evidence of the presence of ammonia or 

 an ammonium salt (it will be seen below that carbon dioxide 

 was present in the blood-plasma). 



Specific Gravity. — This ranged, in the specimens ex- 

 amined, from 1'025 to 1"027. 



Reaction. — The blood when examined immediately after 

 collection was always found to be alkaline to litmus paper. 



Basicity and Acidity. — Observations were made im- 

 mediately after removal of the blood from beneath thoracic or 

 abdominal tergites, great care being taken to avoid injury to 

 viscera. In every case it was found that the blood, which 

 was strongly alkaline to litmus on removal, still remained 



. N , 

 alkaline on adding an efiual volume of t— HCl; on adding an 

 ° oU 



equal volume of ^^^ HCl it became faintly alkaline ; on adding 



an equal volume of - HCl it became acid to litmus paper. 



The basicity of the blood-plasma (which is in part due to 

 ammonium carbonate) is therefore slightly greater than is 



