132 



MICROSCOPIC TECH N IQUKS 



2. Thickness of Sections 



The tissue to be subjected to elementary analysis must be frozen - 

 dried and infiltrated with paraffin by a procedure such as that of 

 Packer and Scott (page 5). Removal of the paraffin from sections 

 of this tissue would involve extractions and displacements of ele- 

 ments by the action of the solutions reciuired. Therefore, it is pref- 

 erable to carry out the absori)tion analysis without removing the 

 paraffin. The absorption of the paraffin itself is demonstrated in 

 Figure 18. The curves were plotted for C2.iH52 (sp. gr. 0.90) ; they 

 show that, up to 3 A, the paraffin may be used in a layer up to 

 50-100 fx, while for 5-6 A the layer should not exceed 10 ju,, etc. 



A summary of Engstrom's calculations of appropriate section 

 thickness for analyses of muscle tissue is given in Figure 19. It is 

 considered prerequisite that the quantity of an element to be 

 analyzed be about twice the smallest quantity which can be deter- 

 mined. Figure 19 was derived from data such as that in Table IV, 



2 



o 



I— 

 < 



< 



1 

 0,8 



0,6 

 0.4 





S02 



z 

 < 

 a: 



0.1 



0.1 



0.2 0.3 



THICKNESS, mm. 



0.4 



0.5 



Fig. 20. Analysis of 

 19 K in muscular tis- 

 sue: (1) Uh; (2) 

 i^/h.; (3) ii/U for 

 /, = /.; (4) ii/io for 

 wavelengths v e r y 

 close to the absorp- 

 tion edge and /, =1-2. 

 See Table IV. 

 From Engalrdi)). 

 (1946) 



which gives the elementary composition of muscle and the mass 

 absorption coefficients and absorption capacity of the elements with 

 the wavelengths used. The wavelength of the K-absorption edge 

 for potassium (atomic number 19) is 3427 X.U. (1 X.U. = 0.001 A), 

 and hence, for the potassium determination analysis lines on each 

 side, 3353 and 3432 X.U. are used in the table. A specific gravity of 

 1.0 for the tissue has been used in the calculation, and the layer 



