MICROSCOPIC STRUCTURE OF THE BLOOD. 



283 



being necessary to burn a portion of the animal tissue in a 

 colorless flame in order to see the bright-red line of lithium : 

 ten minutes after the injection it is found in small quantities in 

 the lens, but plentifully elsewhere ; while four minutes after the 

 injection lithium is not found in the lens, but plentifully in the 

 aqueous humor of the eye, and in the bile. The same rapid 

 diffusion occurs in the human body. The crystalline lenses of per- 

 sons who have been operated upon for cataract have been examined, 

 these persons having previously to the removal of the lens been 

 given by the stomach 20 grains of carbonate of lithium ; in three 

 and a half hours it was detected in each particle of the lens. 



When a sunbeam passes through a glass prism, the differently 



FIG. 152. Spectroscope : P, the glass prism ; A, the collimator tube, showing the 

 slit (s) through which the light is admitted ; B, the telescope for observing the 

 spectrum. 



colored rays which compose it are separated, and if, after emerging 

 from the prism, the beam falls upon a screen, it will appear as a 

 band of different colors, beginning with red and ending with 

 violet; this band is the solar spectrum (Plate 1, Fig. 1). A 

 spectroscope is an instrument for producing and observing spectra 

 (Fig. 152). The beam of light which is to be studied, from what- 

 ever source it may come, passes into the collimator tube A, through 

 the slit s, and its rays, being made parallel by a lens in this tube, 

 are separated or dispersed by the prism p ; the spectrum which 

 results may then be examined by an observer through the telescope 

 B. If the source of the light is an incandescent body, the spec- 

 trum will be a continuous one i. e., there will be nothing but 

 a band of colors, in which the red passes on to violet through 



