PHYSIOLOGICAL 401 



picturesque illustration. In a stream there are two lock-gates, kept 

 in position by powerful springs. The water accumulates above the 

 gates till it drives them open. After the water has rushed through, 

 the springs will come into action again and close the gates. Then 

 the same sequence will be repeated. So is it in the discharge of energy 

 in katabolism. "The molecular aggregates in the suspended, ultra- 

 microscopic spherical droplets of colloidal protoplasm, hold a 

 definite amount of energy which can be liberated by the 'trigger' 

 action. The continuous liquid phase of the living protoplasm will 

 have its dissolved substances in the gaseous state; and, pre- 

 sumably, molecular aggregates of such complex substances as pro- 

 teins could not possibly be so held. It is because of this fact that 

 it is the disperse phase which is supposed to be the seat of the mole- 

 cular aggregates of special architecture, holding definite quantities 

 of potential energy solely as a result of such architecture." The 

 aggregates of molecules break down in katabolism and liberate 

 energy, the liberation being in opposition to the resistance offered 

 by the viscous protoplasm. Then anabolism comes into play, and 

 the special molecular architecture, with its definite quantities of 

 potential energy, is once more reconstituted. Therefore, the dis- 

 charge of energy must be intermittent; the see-saw of anabolism 

 and katabolism must continue rhythmically. We do not suppose 

 that Mr. Sager has said the last word on this difficult question, but 

 he has opened up an interesting line of thought; and its ideas can 

 be extended from the fundamental autonomic rhythm, illustrated 

 by the lock-gates, to superimposed rhythms which are correlated 

 with external periodicities, like those of days and seasons. 



Vital Staining. — It is now generally recognised that a micro- 

 scopic preparation of a living tissue may be a very misleading 

 thing; profound alterations in structure and appearance are inevi- 

 tably caused by the (chemically speaking) rough handling which 

 the living cells receive. First of all, the living matter, semi-fluid and 

 never wholly stable, is "fixed" or violently solidified and probably 

 distorted by powerful chemicals, such as picric acid or corrosive 

 sublimate. Then, perhaps, the water is driven off by alcohol. The 

 alcohol is removed, and the block of tissue immersed in melted 

 paraffin wax. When this has cooled, it supports the frail cellular 

 structures and allows the knife of the microtome to shear off thin 

 regular "sections" — a hundredth of a millimetre or less in thickness. 

 The paraffin is dissolved away when the sections are safely fixed to 

 glass slides, and the process of staining, more or less complex, 

 follows. It remains to drive off the water again and mount the 

 stained sections permanently in balsam or some other preservative. 



Such prepared sections can tell us much of the structure of 

 tissues, for they are easy to decipher; but, as models of the living 

 cells, they must not be trusted too far. Many attempts have been 



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