USE OF THE SPECTROSCOPE. 



21 



the tenth year onwards, the blood of the female is poorer in Hb. The taking of 

 food causes a temporary decrease of the Hb, owing to the dilution of the blood. 



In Animals. In the dog, 9*7 ; ox, 9*9 ; sheep, 10'3 ; pig, 127; horse, 131 ; birds, 16-17 

 per cent. 



Pathological. A decrease is observable during recovery from febrile conditions, and also 

 during phthisis, cancer, ulcer of the stomach, cardiac disease, chronic diseases, chlorosis, 

 leukaemia, pernicious anaemia, and during the rapid mercurial treatment of syphilitic persons. 



14. THE SPECTROSCOPE. As the spectroscope is frequently used in the investigation of 

 blood and other substances, a short description of the instrument is given here (fig. 16). It 



A, tube ; S, slit ; m, m. 



B, eye of observer looking 



Fig. 16. 

 Scheme of a spectroscope for observing the spectrum of blood, 

 layer of blood with flame in front of it ; P, prism ; M, scale 

 through a telescope ; r, v, spectrum. 



consists of (1) a tube, A, which has at its peripheral end a slit, S (that can be narrowed or 

 widened). At the other end a collecting lens, C (called a collimator), is placed, so that its 

 focus is in exact line with the slit. Light (from the sun or a lamp) passes through the slit, and 

 thus goes parallel through C to (2) the prism, P, which decomposes the parallel rays into a 

 coloured spectrum, r, v. (3) An astronomical telescope is directed to the spectrum r, v, 

 and the observer, B, with the aid of the telescope, sees the spectrum magnified from six to 

 eight times. (4) A third tube, D, contains a delicate scale, M, on glass, whose image, when 

 illuminated, is reflected from the prism to the eye of the observer, so that he sees the 

 spectrum, and over or above it the scale. To keep out other rays of light the inner ends of 

 the three tubes are covered by metal or by a dark cloth (see also 265). 



[The micro-Spectroscope, e.g., as made by Browning or Zeiss, may be used when small quan- 

 tities of a solution are to be examined. Every spectroscope ought to give two spectra, so that the 

 position of any absorption-band may be definitely ascertained. The spectroscope is fitted into 

 the ocular end of the tube of a microscope instead of the eye-piece. Small cells for containing 

 the fluid to be examined are made from short pieces of barometer-tubes cemented to a plate of 

 glass.] 



Absorption Spectra. If a coloured medium {e.g., a solution of blood) be placed between the 

 slit and a source of light, all the rays of coloured light do not pass through it some are 

 absorbed ; many yellow rays are absorbed by blood, hence that part of the spectrum appears 

 dark to the observer. On account of this absorption, such a spectrum is called an " absorption 

 spectrum. " 



Flame Spectra. If mineral substances be burned on a platinum-wire in a non-luminous 

 flame or Bunsen's burner in front of the slit, the elements present in the mineral or ash give 

 special coloured band or bands, which have a definite position. Sodium gives a yellow, 

 potassium a red and violet line. These substances are found on burning the ashes of almost 

 all organs. 



If sunlight be allowed to fall upon the slit, the spectrum shows a large number of lines 



