54 BOTANY 



compounds are formed. Coagulating reagents, accordingly, play an important part 

 in microscopic technique ; of especial value are such which, while fixing and 

 hardening the protoplasm, change its structure in the least degree. As a fixing 

 and hardening reagent for vegetable tissues, alcohol is particularly serviceable ; 

 under certain conditions, sublimate alcohol, or 1 to 2 per cent formaldehyde. 

 For animal cells and for the lower plants, 1 per cent chromic acid, 1 per cent 

 acetic acid, 0'5 to 1 per cent osmic acid, concentrated picric acid, or corresponding 

 mixtures of these acids, and also formaldehyde, are used for the same purpose- 

 Iodine stains protoplasm brownish yellow ; nitric acid, followed by caustic potash, 

 yellowish brown ; sulphuric acid, if sugar be present, rose red. Acid nitrate of 

 mercury (Millon's reagent) gives to protoplasm a brick-red colour. Treated with 

 copper sulphate, followed by caustic potash, protoplasm is coloured violet ; with 

 an aqueous or alcoholic solution of alloxan, red. Aromatic aldehydes in the 

 presence of a reagent for effecting condensation, such as sulphuric or hydrochloric 

 acid, and an oxidising substance or a 'higher chloride, also produce in protoplasm 

 characteristic colour reactions ; thus, benzaldehyde gives a blue-green to blue ; 

 piperonal, a violet-blue ; vanillin, a violet or violet-blue reaction. Protoplasm is 

 soluble in dilute caustic potash and also in eau de Javelle (potassium-hypo- 

 chlorite), and accordingly both of these reagents may be recommended for clearing 

 specimens, when the cell contents is not to be investigated. All of the above- 

 mentioned reagents kill protoplasm ; until they have done so, their characteristic 

 reactions are not manifested. In their greater or less resistance to the action of 

 solvents, in the degree of their sensitiveness to reagents, and in the intensity of the 

 reactions, the various constituents of protoplasm, cytoplasm, nucleus, centrospheres, 

 and chromatophores differ from one another, and thus a means of determining 

 their component substances is afforded. Accordingly a large number of albuminous 

 bodies or albuminates have been named which are said to enter into the composi- 

 tion of living protoplasm. It is worthy of note that these compounds, although 

 still for the most part not fully determined, all contain phosphorus. Such as are 

 peculiar to the nucleus have been comprehended under the term ntjclein". Stain- 

 ing reagents have also become an important help to microscopic investigations for 

 determining the composition of protoplasm. This is due to the fact that the 

 different constituents of protoplasm take up and retain the stain with different 

 degrees of intensity and energy. As a general rule, only coagulated protoplasm 

 can absorb colouring matter, although some few aniline stains can, to a limited 

 extent, permeate living protoplasts. For staining vegetable protoplasts, which 

 have been previously hardened, the various carmines, hsematoxylin, iodine green 

 acid fuchsin, eosin, methylene blue, and aniline blue, have been found particularly 

 convenient. The different components of the protoplasm absorb the stains with 

 different intensities, and, when reagents are employed to remove the colouring 

 matters, they exhibit differences in their power to retain them. The nucleus 

 generally becomes more intensely coloured than the rest of the protoplasm, 

 especially a part of its substance, which is therefore called Chromatin. The 

 chromatin, moreover, is not affected by gastric juices nor by solutions of pepsin 

 containing hydrochloric acid, although both cytoplasm and chromatophores are 

 at once digested by them. On the other hand, with a trypsin solution, chromatin 

 is quickly dissolved. In addition to those substances, which are to be regarded 

 as integral parts of active protoplasm, it always includes derivative products of 

 albuminates, particularly amides, as asparagin, glutamin ; also ferments, as 

 diastase, pepsin, invertin ; at times alialoids, and always carbohydrates and fats. 

 The ash left after incineration also shows that protoplasm always contains mineral 

 matter, even if only in small quantities. All substances which, as such, do not 



