ZOOLOGY AND BOTANY, MIOEOSCOPY, ETC. 757 



Pigmented bodies. — The influence of chemical agents on the pig- 

 ment-bodies of protoplasm has been much studied ; nevertheless 

 but few reagents are known. Etiolin becomes blue when treated 

 with sulphuric acid or chlorine water ; the green substance to which 

 the name of chlorophyll is now appropriated turns yellow under the 

 prolonged action of diluted acids, whilst concentrated hydrochloric 

 and sulphuric acids colour it blue or blue-green. The use of hydro- 

 chloric acid or of water at 50° C. is recommended for isolating 

 hypochlorine, and potash for colouring brown anthoxanthin and 

 madder,* and chloride of iron to turn this last substance red or orange. 

 But here ends our knowledge of the reagents for these substances, 

 whose study presents great interest for physiology, agriculture, and 

 manufactures. 



Proteid Crystalloids. — The colouring which these bodies take 

 under the influence of certain reagents, helps, independently of other 

 characters, to distinguish them from mineral crystals. " Their sub- 

 stance exhibits," says Sachs, "all the more essential reactions of 

 protoplasm, its power of coagulation and of taking up colouring 

 matters, the yellow reaction with potash after treatment with nitric 

 acid, as well as that with iodine."! 



Eecourse is also had to these a,gents to diagnose the crystalloids 

 of protoplasm when they are colourless, like those of the potato, 

 LatJircea squamaria, the aleurone grains of oleaginous seeds and of the 

 albumen of castor-oil. In the petals of the pansy {Viola tricolor) 

 and the orchids, the fruits of Solanum americanum and the sporangi- 

 ferous filaments of Piloholus, when they are coloured, they may be 

 decolorized by alcohol, and then coloured afresh by the agents just 

 mentioned. 



2. Ternary Substances. 



Starch. — Iodine is the best reagent for starch. It is generally 

 said in treatises on chemistry that it turns it blue. It is important 

 to know under what conditions this takes place. When the starch- 

 granules of the haricot bean, for instance, are subjected to an aqueous 

 solution of iodine they immediately turn blue. But it must be 

 remarked that : — 1st. The colouring disappears under the influence 

 of great heat, and reappears when cold again. 2nd. The blue 

 colour of the granules is only due to a portion of the substance 

 which composes it. The amylose can be distinguished in each 

 granule, of which it forms in some degree the skeleton, as also the 

 granulose which fills the interstices, and may be extracted by diastase. 

 The former turns yellow, whilst the latter turns a deep blue under 

 the action of iodine. Most frequently they exist together ; but there 

 are cases in which they are isolated. The amorphous starch of 

 Bacillus amylobacter and of Spirillum amyliferum is entirely composed 

 of granulose ; iodine colours it blue. In the Florideae starch exists 

 in the form of grains of pure amylose to which a solution of iodine 

 gives a yellow colour. When, as in the potato, amylose and granulose 



* Decaisne, 'Kecherches auatomiques et physiologiques sur la Garance,' &c., 

 (10 pis.) 1837. 



t Loc. cit,, p. 49. 



