ZOOLOGY AND BOTANY. MICROSCOPY, ETC. 245 



The result of the first five measurements added together give the 

 length of the parasite. For the sake of comparison the mean of each 

 of the above five measurements of Trypan osomata of any one species 



Fig. 37. 



are first taken, and then the percentage value of each measurement is 

 calculated, taking the mean total length as 100. 



This method affords a basis for the comparison of the various 

 species. 



Metallography, etc. 



Pressure and Percussion Figures on Plastic Crystalline Metals.* 

 It is known that figures of definite form, related to the orientation of 

 the crystal, are developed by forcing a sharp point into brittle crystalline 

 substances. F. Osmond and Gr. Cartaud have employed the same method 

 on metallic crystals. The point of a sewing-needle was pressed by 

 means of a lever into the faces obtained by cutting a crystal of iron in 

 different planes. The pressure employed was 1600 grm. The figures 

 were examined microscopically, and are described by the authors, with 

 diagrams and photomicrographs. The method may be put to practical 

 use in determining the orientation of crystals, sections of which are 

 exposed in a polished metallic surface. 



Nickel-Vanadium Steels.f — L. Guillet has examined 32 steels con- 

 taining 2—30 p.c. nickel, * 2-7 ' 5 p.c. vanadium, 0" 14-1* 2 p.c. carbon. 

 He classifies them in six groups : (1) pearlitic ; (2) containing carbide 

 and ferrite ; (3) martensitic ; (4) containing martensite and carbide ; 

 (5) containing y-iron ; (6) containing y-iron and carbide. Vanadium ex- 

 hibits the tendency, previously observed in vanadium steel, to combine 

 with the carbon, forming a carbide. The effect of vanadium upon 

 mechanical properties is beneficial only in the case of pearlitic steels, in 

 which the maximum tensile stress and elastic limit are raised. The 

 favourable effect is intensified by suitable heat treatment. Addition of 

 vanadium to y-iron steels diminishes their capacity of resisting shock. 



Nitrogen in Steel. f — In view of the interest aroused by H. Braune's 

 recent researches, translations or reprints of three papers are here given. 

 In the first, by H. Tholander, originally published in 1888, differences 



* Rev. Metallurgie, ii. (1905) pp. 811-15 (9 figs.), 

 t Tom. cit., pp. 870-81 (16 photomicrographs). 

 X Tom. cit., pp. 882-99. 



