USE OF THE SPECTROSCOPE. 27 



value of each corpuscle was | or of the normal. Variations in the amount of 

 haemoglobin may be recorded on the same chart as that employed for the corpuscles. 



In using the instrument, the tint may be estimated by holding the tubes between 

 the eye and the window, or by placing a piece of white paper behind the tubes ; 

 the former is perhaps the best. Care must be taken that the tubes are always 

 held in the line of light, not bejow it. In the latter case some light is reflected 

 from the suspended corpuscles from which the haemoglobin has been dissolved. 

 If the value of the corpuscles is small, then a perceptibly paler tint is seen when 

 the tubes are held below the line of illumination. If all the light is transmitted 

 directly through the tubes, the corpuscles do not interfere with the tint. 



In using the instrument it will be found that, during 6 or 8 degrees of dilution, 

 it is difficult to distinguish a difference between the tint of the tubes. It is there- 

 fore necessary to note the degree at which the colour of the dilution ceases to be 

 deeper than the standard, and also that at which it is distinctly paler. The degree 

 midway betweeu these two will represent the haemoglobin percentage. 



The instrument is only expected to yield approximate results, accurate within 

 2 or 3 per cent. It has, however, been found of much utility in clinical observa- 

 tion."] 



The amount of haemoglobin in man is 12 to 15 per cent., in the 

 woman 12 to 14 per cent., during pregnancy 9 to 12 per cent. 

 (Preyer). According to Leichtenstern, Hb is in greatest amount in 

 the blood of the newly-born infant, but after ten weeks the excess 

 disappears. Between six months and five years, it becomes least in 

 amount, reaches its second highest maximum between twenty-one 

 and forty-five, and then sinks again. From 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. 



Pathological. A decrease is observable during recovery from febrile condi- 

 tions, 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, Use of the Spectroscope. 



As the spectroscope is frequently used in the investigation of blood and other 

 substances of the body, it will be convenient to give a short description of the 

 instrument here (Fig. 10). It 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 Blood in urine). 



[The micro-spectroscope, e.g., that known as the " Sorby-Browning " micro- 

 spectroscope is very useful when small quantities of a solution are to be examined.] 



