VISIBLE AND U.V. ABSORPTION HISTOSPECTROSCOPY 



119 



accurate technique is used. A quartz plate 1 mm. thick and 2 cm. 

 square is placed in the path of the monochromatic beam at an angle 

 of 45° and at a distance from the telescope lens of 46 cm. (Fig. 10 L 

 By this means 6-7 % of the incident radiation is reflected to another 

 photocell mounted at a distance from the quartz plate equal to that 

 of the aperture of the microscope condenser. The photocell output is 

 amplified by a Huntoon (1935) direct-current amplifier and passed 

 through a Leeds and Northrup type P wall galvanometer. Simul- 

 taneous readings are taken on the same scale, from both this gal- 

 vanometer and the one used for recording transmission, at each 

 wavelength without moving the object, but with careful focusing of 

 condenser and objective at each wavelength. After these readings 

 are obtained the object is moved away and the readings for the 

 clear quartz slide are taken. The data are used to calculate the 

 transmission and extinction coefficients as usual. 



in 



ro 



o CM 



n CO 



rt o 



ro m 



'J- ^ 



(T> o 



00 00 



C\J CM 



cvj i^ m o 



ID on CO o 



^ Ln ^ ^ 



CM CM CM CM 



WAVE LENGTH, A 



Fig. 11. Absorption curve of colloid in a single 

 follicle of a thyroid gland in alkaline (^1) and acid 

 (.42) medium, as compared with the ultraviolet ab- 

 sorption curves of extracted sheep thyroglobulin 

 made by Ginsel in alkaline (fil) and acid medium 

 (B2). From Gersh and Baker (1943) 



The reliability of the technique is shown by Figure 11, taken 

 from Gersh and Baker (1943). The curves in the inset (B) were 

 obtained by Ginsel (1939) for extracted sheep thyroglobulin in both 

 acid and alkaline media, while those in (A) were established by 

 Gersh and Baker by their histospectrographic technique on the 

 colloid in a single thyroid follicle. 



