DIV. i MORPHOLOGY 15 



ing phosphorus (nucleo-proteids) predominate ; these are not dissolved 

 by pepsin, and only with difficulty by trypsin. Products of the dis- 

 sociation of proteids, especially amides, are also contained in the 

 protoplasm. Other components are enzymes, carbohydrates, and 

 lipoids, such as fats and lecithin, in the condition of a fine emulsion ; 

 phytosterin (aromatic alcohols with the formula C 2l? .H 45 OH), and 

 sometimes alkaloids and glucosides. The ash left after incineration 

 shows that mineral substances are not wholly wanting in the 

 protoplasm. 



By the action of a dilute solution of potash, of chloral hydrate, or of eau de 

 javelle, all parts of the protoplast are dissolved. Iodine stains it a brownish-yellow 

 colour ; acid nitrate of mercury (Millon's reagent), rose-red: Such reagents kill 

 the protoplasm, afte/ which their characteristic reactions are manifested. These 

 reactions are given by proteid substances, but are not altogether confined to them. 



D. Structure of the Parts of the Protoplast 



Great assistance in the investigation of the structure of the proto- 

 plast is afforded by the processes of fixing and staining. Certain 

 fixing agents harden and fix the protoplasm almost unaltered, but 

 it is necessary to be on guard against the appearance of a structure 

 in the process of coagulation ( 9 ). 



The importance of staining depends upon the fact that the various constituents 

 of the protoplast absorb dyes with different intensity and hold them more or less 

 firmly when the preparation is washed. As a general rule only dead protoplasm 

 is readily stained. For staining fixed vegetable protoplasts, solutions of carmine, 

 haematoxylin, safranin, acid fuchsin, gentian violet, orange, methylene blue, etc., 

 are employed. 



1. The Cytoplasm. This when highly magnified is seen to con- 

 sist of a clear, hyaline, more or less tenacious fluid (HYALOPLASM) in 

 which more or less numerous minute drops or granules (MICROSOMES) 

 are embedded. The latter evidently are various products of the 

 metabolism, and characterise the granular protoplasm or POLIOPLASM. 

 The hyaloplasm itself is, however, not a simple solution. AVhen 

 investigated with the help of the ultra-microscope, an instrument 

 which reveals granules and droplets too minute to be seen with the 

 highest powers of the ordinary microscope, it is found to contain 

 countless numbers of ultra-microscopic particles ( 10 ). This is a general 

 characteristic of those solutions which the physical chemist recognises 

 as COLLOIDAL SOLUTIONS or SOLS. The demonstration that protoplasm 

 is a colloidal solution, and, in fact, an emulsion, is of fundamental 

 importance. By its help many vital manifestations become susceptible 

 of a physico-chemical explanation. 



An extremely thin boundary layer free from granules is found at 

 the periphery of the protoplast, and a similar layer bounds every 

 vacuole present in the cytoplasm. The peripheral boundary layer and 



