A STUDY OF THE BLOOD OF CERTAIN COLEOPTEKA. 155 



precipitated on cent;rifugalisation. In addition numerous 

 ultra-microscopic particles of much smaller size were recog- 

 nisable on strong illumination against a dark background. 

 The former granules when a film of blood was prepared by 

 Leishman's metliod (alcohol fixation, staining with methylene- 

 blue-eosin) stained blue. 



Grases Dissolved in Blood. — 1*65 c.c. of blood-plasma 

 (obtained from seventeen Dytisci) were placed in con- 

 nection with a Toepler pump and '14 c.c. of gases extracted. 

 On exposing this to the action of a 10 per cent, solution of 

 caustic potash the volume was reduced by '11 c.c. On 

 adding a 50 per cent, solution of caustic potash containing 

 2'3 per cent, of pyrogallol a very slight diminution of volnme, 

 too small to determine, occurred, and "03 c.c. of gas remained 

 behind, representing nitrogen and argon. The percentage 

 amounts of dissolved gases were therefore : 



Carbon dioxide .... 6"7 per cent. 



Nitrogen . . . . .1*8 ,, 



Total . . . .8-5 



Characters op the Blood-Plasma of Hydrophilus Piceus. 



Colonr and Spectroscopic Appearance. — Immedi- 

 ately after collection the blood was, in a layer four millimetres 

 thick, of a straw-yellow^ colour. Subsequently it became 

 dark brown, the change first appearing at the upper surface, 

 in contact with the air. When kept in hydrogen the blood 

 remained for several hours of a pale yellow colour, whence it 

 follows that the darkening is due to absorption of oxygen. 

 The tension of dissolved oxygen in the blood must, therefore, 

 be very low. On spectroscopic examination of the blood in a 

 layer 18 mm. thick a general darkening of the spectrum was 

 observed, the extent of the spectrum diminishing towards 

 both the red and the blue, but no absorption bands were 

 visible. When darkening- of the blood occurred on standing- 



