482 PRACTICAL PHYSIOLOGY 



suction filter plate and sucked dry. It is washed with water three 

 times. The washings are then transferred to a 2 litre flask, nearly 

 neutralised and boiled down to a small volume (50 c.c.) with the flask 

 on the slant. The evaporated washings are then mixed with the 

 contents of the evaporating dish (the evaporated supernatant fluid) 

 and the whole brought to a volume ,of 50 c.c., after which it is cooled, 

 almost neutralised, filtered through a small filter paper, the filter 

 washed and the volume of the filtrate and washings brought up to 

 100 c.c. The sugar is then estimated in this by one of the methods 

 described on page 274. 



CHAPTER XVI. 



THE PHOTOGRAPHIC SPECTRA OF HAEMOGLOBIN AND ITS 

 DERIVATIVES. THE SPECTROPHOTOMETER. 



Photographic Spectra of Haemoglobin. Certain absorption bands 

 in the violet end of the spectrum are characteristic of haemoglobin 

 and its derivatives. These may be demonstrated by photographing 

 the violet end when solutions of haemoglobin or certain of its 

 derivatives are placed between the slit and the source of light. They 

 may also be shown by projecting the rays issuing from the telescope 

 upon a fluorescent screen according to the following method. 



Very considerable illumination is required. A beam of sunlight 

 projected by a heliostat is probably the best illumination as certain of 

 the Fraunhof er lines (H & K) may be seen, though indistinctly, and thus 

 fix the position of the absorption bands appearing. In default of this 

 an electric arc lamp may be used, and if actuated by the continuous 

 current the positive pole should be arranged to send a beam through 

 the slit of the collimator of an ordinary compound spectroscope. The 

 slit must be opened very widely. The eyepiece of the telescope is 

 removed, and the issuing rays can be focussed on a screen having a 

 coating of barium platino-cyanide fixed a few inches from the eye- 

 piece. The spectrum, with the beam from the positive pole of an arc 

 lamp, is continuous, but if the arc lamp, using an alternating current, be 

 adopted, certain absorption bands will be seen in the green fluorescence 

 which replaces the violet end. They do not greatly interfere, however, 

 with the development of the absorption bands characteristic of oxy- 

 haemoglobin and the haemoglobin derivatives, and these bands appear- 





