104 Physiologie. — Eumycetes. 



The author points out that the apparatus described requires 

 only a small outlay to Supplement the ordinary equipment of a phy- 

 siological laboratory, W. Neilson Jones, 



3rown, H. T., Some studies on yeast. (Ann. of Bot. XXVIII. 

 p. 197-226. 8 figs. 1Q14.) 



The author besides presenting new experimental results dis- 

 cusses throughout the paper the results and conclusions of other 

 writers regarding the two topics dealt with, namely, 1) the relation 

 of cell reproduction to the supply of free oxygen, 2) the metabolism 

 of the yeast cell with special reference to the thermal phenomena 

 of fermentation. Under the lirst heading the main facts experimen- 

 tally established concerning the reproduction of yeast cells in a 

 nutrient liquid containing dissolved oxygen and excess of all the 

 mineral and organic substances requisite for füll nutrition are thus 

 summarised. When the available oxygen is limited to that initially 

 contained in the liquid, the number of cells per unit volume tends 

 to reach a maximum that is independent or nearly so of the num- 

 ber of cells of seed-yeast per unit volume, but is conditioned in the 

 tirst instance by the initial amount of this dissolved oxygen. Within 

 certain limits of oxygen supply, the maximal reproduction is strictlj^ 

 proportional to the initial amount of this oxygen. The rate of repro- 

 duction under these conditions is a linear function of the time. The 

 dissolved oxygen does not remain as such in the liquid during the 

 reproductive period, but is rapidly absorbed by the seed-yeast 

 before budding begins — the author considers that this fact and 

 all that it implies provides a satisfactory explanation of all the 

 phenomena dealt with. In the second part of the paper the author 

 raises the question of the significance of the enormous metabolism 

 and liberation of energy shown by the yeast cell (as indicated b}' 

 its evolving heat rapidl3^ enough to raise its temperature 106° C. 

 per hour), which seem so disproportionate to its requirements for 

 reproduction and nutrition. He suggests that the explanation lies in 

 the fact that the conditions under which yeast is usually cultivated — 

 namely, in relatively large masses of liquid containing a limited 

 oxygen supply — are eminently artificial. differing entirelv trom 

 the natural conditions under which the specific ph3'siological cha- 

 racters of the Sacchnromycetes have been evolved. In nature yeasts 

 grow in media rieh in all requisite nutrient substances and with 

 the ready and continuous access of oxj'gen, hence extremeh' rapid 

 multiplication occurs, which has not the check imposed upon it 

 that it has when cultivations are made on a large scale in brewing. 

 This rapid and constant building up of new cells, under continued 

 action of oxygen, requires a constant source of extraneous energy 

 furnished by the auxilliary fermentative function of the cells, and 

 since the growth proceeds in a medium of high specific heat and 

 under conditions involving a natural tendency for rapid equalisation 

 of temperature with the surrounding, it is ndvantageous for yeast 

 to have some other and more intense energy-source than that sup- 

 plied by the respiratory processes. Hence by a stud}»^ of these natural 

 cases it becomes easier to understand the true relation of the fer- 

 mentative to the reproductive processes, and why the yeast have 

 acquired their fermentative power. That we can b}' more or less 

 artificial means keep the reproductive power of yeast in abeyance, 

 while still availing ourselves of its fermentative power, has hitherto 



