ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



.lilil 



water 10 litres; magnesium chloride 1 kilo; sodium fluoride 0*2 kilo. 

 In tins fluid zoological preparations, especially reptiles, preserve tbeir 

 natural colours, as also do most anatomical preparations. Should the 

 preserved material require to be sectioned, it must be treated with water 

 3 or 4 times to extract the preservative ami then immersed in alcohols 

 of increasing strength. If soap be used the material may be imbedded 

 direct. 



Colloid Form of Piperine, its Refractive and Dispersive Powers.* 

 — H. G. Madan has found that, in order to ensure with approximate 

 certainty the conversion of crystalloid piperine into colloid piperine, an 

 exposure to a temperature of not much less than 180° for a period of 

 not much less than one hour is required. Prepared in this way piperine 

 will retain for at least 2r> years the colloid condition without alteration, 

 closely resembling ordinary " rosin " (colophony) in appearance, but not 

 quite so brittle. 



Colloid piperine possesses a higher refractivity than most other resins 



Fig. 130. 



Piperine. 



K a 



h 



D 



H/J 



I 



Glass. 



Ka Ha D E 



Comparative length of tloe spectra of piperine and glass. 



Hp h, 



or resin-like substances, and its dispersive power is still more remarkable, 

 = 0-142. The diagram (fig. 130) shows the extent of the piperine 

 spectrum as compared with that given by a prism of dense flint glass 

 having the same refracting angle. From its high refractivity piperine 

 seemed likely to be useful in the construction of certain kinds of 

 polarising prisms, but owing to the extraordinarily high dispersive power, 

 the critical angles for the different rays of the visual spectrum differ so 

 widely that the prism is practically useless unless monochromatic light 

 be employed. 



(6) Miscellaneous. 



Polarised Light for Investigating Nerve-Fibres. f—K. Brodmann 

 has investigated the appearances of normal and of degenerated nerve- 

 fibres by the aid of polarised light. The principal feature of normal 

 nerve-fibres was their strongly negative double refraction, while degene- 

 rated nerves lost this attribute in proportion to the amount of degenera- 



* Trans. Chem. Soc, lxxix. (1901) pp. 922-7 (1 fig.). 

 t Neurol. Centralbl., xix. (1900) p. 1154. 



