PHYSIOLOGICAL 399 



elastic term it is probably true. In any event these cases are too 

 exceptional and too little understood for further discussion here. 



A difficult point in the chemistry of cells is the amount of 

 chemical activity which goes on in certain cells, such as the red 

 blood corpuscles of birds, which do not seem to have anything to 

 show for it. They do not contract, they are not specially concerned 

 in the receiving of stimuli, they do not grow nor form special sub- 

 stances as far as we can tell, yet they consume appreciable quantities 

 of oxygen and food material. Warburg has suggested that the cell 

 requires a constant supply of energy to maintain an essential ultra- 

 microscopic structure within the protoplasm — possibly something 

 of the nature of a film net. For chemistry this is a convenient idea, 

 as it is difficult to see how so many different reactions can go on 

 in a single cell in the absence of partitions of some sort; while the 

 surfaces of such partitions might very well be the site of the reac- 

 tions. It has already been pointed out that the network visible in 

 stained and fixed cells is the unnatural result of very artificial 

 treatment; and also that to the micro-dissecting needle protoplasm 

 is apparently structureless and fluid. Moreover, if a dye be injected 

 into the cell it spreads rapidly through the whole, and the fact that 

 protoplasm conducts electricity is a sign that metallic and acid ions 

 of the dissolved salts always present have an equal freedom of 

 movement. It is possible that reactions in cells go on chiefly at 

 surfaces, e.g. between "pure" protoplasm and its inclusions, like 

 granules and vacuoles and mitochondria; on the external surface 

 of the cell; on the surface of the nucleus, and so on; and that 

 between these is a surrounding ocean of inactive protoplasm per- 

 meable to dyes and salts; nor is it impossible that to maintain such 

 surfaces energy is required. It is certain that an injury to the cell 

 causes the external membrane to become less efficient. Surface is 

 undoubtedly of great importance in reactions within the cell, and 

 protoplasm, like any other complex colloidal system, has a great 

 tendency to form films at surfaces; hot milk is an extreme case of 

 this property of colloids. 



Warburg has, in any case, won a leading place in the study of 

 the relation between the activity and the structure, whatever it is, of 

 the cell. If cells are ground up and destroyed mechanically, without 

 interfering with their chemical constituents (if this is possible), the 

 structureless living matter continues for some time to consume 

 oxygen and yield carbon dioxide; but enormously less than in the 

 intact cell, and only in the presence of some more or less solid frag- 

 ments. This is further evidence for the importance of surfaces in 

 the chemical life of the cell. 



RHYTHM OF THE CELL —It is in some cases evident that the 

 dominant metabolism of a cell does not proceed continuously, but 



