98 WEIGERT'S HYPOTHESIS 



protoplasm. The whole process is explained as one of perverted 

 nutrition, and (once admitting Ehrlich's theory of the constitution 

 of the molecule of protoplasm and of the way it is nourished) 

 without introducing any but well-recognized biological pheno- 

 mena. The theory is fascinating in its simplicity, and although 

 there are a few difficulties in the way of its full acceptance as a 

 complete explanation of the facts, it certainly accounts for them 

 far better, on the whole, than any other theory will do if, indeed, 

 an alternative one has been put forth. And it has the great merit 

 in a theory that its application has led to the discovery of new 

 facts. ' 



A few remarks are necessary in connection with the question 



FIG. 24. 



of the mechanism in which the over-production of side-chains is 

 produced. Weigert's hypothesis with regard to the nature of 

 hyperplasia as the result of injury or irritation is now well known, 

 and a brief outline will suffice. He imagines that the maintenance 

 of the normal structure and physiological function of a tissue 

 depends upon a condition of equilibrium brought about by a 

 series of mutual restraints exerted by each cell on its neighbours. 

 In the same way, the structure of a single cell, or perhaps of a 

 single compound molecule of protoplasm, depends on a similar 

 equilibrium existing between minute living units. If one of these 

 components is killed or injured, the restraint which it exerts on 

 the surrounding units is removed, and unrestrained growth can 



