246 STUDIES ox FEKMEXTATIOX. 



in their extreme states. The progressive changes in the cells, 

 after they have acquired their normal form and volume, clearly 

 demonstrate the existence of a chemical work of a remarkable 

 intensity, during which their weight increases, although in vo- 

 lume they undergo no sensible change, a fact that we have often 

 characterized as " the continued life of cells already formed." 

 "\Ve may call this work a process of maturation on the part of 

 the cells, almost the same that we see going on in the case 

 of adult beings in general, which continue to live for a long 

 time, even after they have become incapable of reproduction, 

 and long after their volume has become permanently fixed. 



This being so it is evident, we repeat, that, to multiply in a 

 fermentable medium, quite out of contact with oxygen, the cells 

 of yeast must be extremely young, full of life and health, and 

 still under the influence of the vital activity which they owe to 

 the free oxygen which has served to form them, and which they 

 have perhaps stored up for a time. When older, they repro- 

 duce themselves with much difficulty when deprived of air, and 

 gradually become more languid ; and if they do multiply, it is 

 in strange and monstrous forms. A little older still, they 

 remain absolutely inert in a medium deprived of free oxygen. 

 This is not because the}'^ are dead ; for in general they may be 

 revived in a marvellous manner in the same liquid if it has been 

 first aerated before they are sown. It would not surprise us to 

 learn that at this point certain preconceived ideas suggest them- 

 selves to the mind of an attentive reader on the subject of the 

 causes that may serve to account for such strange phenomena in 

 the life of these beings which our ignorance hides under the 

 expressions of youth and age ; this, however, is a subject that 

 we cannot pause to consider here. 



At this point we must observe — for it is a matter of great im- 

 portance — that, in the operations of the brewer there is always a 

 time when the yeasts are in this state of vigorous youth of 

 which we have been speaking, acquired under the influence of 

 free oxygen, since all the worts and all the yeasts of commerce 

 are necessarily manipulated in contact with air, and so impreg- 



