ITS CHEMICO-PHYSICAL AND MORPHOLOGICAL PROPERTIES 17 



proteids are the most complex of all known organic substances, 

 but up till now very little has been determined as to their chemical 

 structure. This complex structure depends, in the first place, upon 

 the very remarkable chemical properties of carbon (Haeckel II. 15). 

 In proteids carbon occurs combined with four other elements, 

 hydrogen, oxygen, nitrogen, and sulphur, in proportions which, 

 it has been endeavoured to express by the following formula : C 72 

 H 106 N 18 SO- 2 (composition of a molecule of egg-albumen). 



Amongst the various kinds of proteid bodies (albumins, globu- 

 lins, fibrins, plastins, nucleins, etc.) plastin alone seems to be pecu- 

 liar to protoplasm (Reinke II. 32; Schwarz II. 37; Zacharias 

 II. 44) ; plastin is insoluble in water, in 10 per cent, salt solution, 

 and in 10 per cent, solution of sulphate of magnesia ; it is pre- 

 cipitated by weak acetic acid, whilst concentrated acetic acid 

 causes it to swell up ; it is precipitated in concentrated salt 

 solution ; it resists both pepsin and trypsin digestion. It is hardly, 

 or not at all, stained by basic aniline dyes, but is stained by 

 acid ones (eosin and acid fuchsine). 



In addition, globulins and albumins are present in smaller 

 quantities ; these are also found in solution in the cell-sap of 

 plants. 



Protoplasm is very rich in water, which, as Sachs (II. 33) states, 

 is built up into the structure of its molecule, in the same sense as, 

 for example, the water of crystallisation is a necessary constituent 

 of many crystals, which lose their characteristic form if the water 

 of crystallisation is withdrawn. Reinke (II. 32) found 71'6 per 

 cent, of water and 28'4 per cent, of solid substances in fresh 

 sporangia of the ^Ethaiium septicum (66 per cent, of this water 

 could be squeezed out). 



Further, a number of various salts are present in protoplasm ; 

 these remain as ash when the protoplasm is burnt ; in the case of 

 the JEthalium septicum, the ash contains the following elements : 

 chlorine, sulphur, phosphorus, potassium, sodium, magnesium, 

 calcium, and iron. 



Living protoplasm is distinctly alkaline in reaction ; red litmus 

 paper is turned blue by it, as is also a red colouring matter, which, 

 is obtained from a species of cabbage, and which has been used by 

 Schwarz. This is also the case with plants, although the cell-sap, 

 as a rule, has an acid reaction. According to the investigations 

 of Schwarz (II. 37) on plants, this alkaline reaction is due to the 

 presence of an alkali, which is united with the proteid bodies in 



c 



