PROTOPLASM 413 



claiming any attempt to trace a fanciful connection between 

 the colloidal metal solutions and enzymes, emphasizes the fact 

 that the two properties of catalytic action and colloidal nature 

 are common to both classes of compounds and regards the 

 colloidal metals as the simple inorganic analogues of the more 

 complex enzymes. 



One further illustration might be quoted of the chemical 

 activity which is associated with colloidal substances presenting 

 a large surface. A calculation based on the assumption that 

 there are five million red blood corpuscles of diameter -007 mm. 

 contained in i c.mm. of blood reveals the striking fact that 

 the total surface presented by the blood corpuscles contained 

 in 5 litres of blood (the amount contained in the body of a 

 full-grown man) would be about 1875 square metres. From 

 what has gone before it is, therefore, not surprising that these 

 corpuscles should be endowed with special properties enabling 

 them, in the presence of the trace of iron which they contain, 

 to play their part in the highly complex changes involved in 

 respiration. 



THE COLLOIDAL NATURE OF PROTOPLASM. 



From the foregoing consideration of the colloidal state, it 

 is obvious that this condition endows matter with great powers, 

 the exercise of which are dependent on the particular phase of 

 the colloid, the presence of substance amenable to change, 

 and the appropriate conditions for the action to take place. 



From the biological point of view protoplasm is the all- 

 important colloid, for it is in protoplasmic activity that the 

 key to all vital actions and reactions are to be found. 



In earlier days the structure of protoplasm was variously 

 described as alveolar, reticulate, fibrillar, and so on. These 

 views were based on the observation of living protoplasm by 

 the ordinary methods of microscopy, and on dead protoplasm 

 fixed and stained by the ordinary methods of cytological 

 technique. Many of the characters observed by the latter 

 method were artifact, and from the former pursuit too little 

 was observable although it was realized, perhaps dimly, that 

 protoplasm was possessed of colloidal characters. 



