88 THE AMERICAN MONTHLY [March 



which is inimical to the further growth of the yeast, 

 a pheiiomenoD which is of frequent occurrence. But 

 the bacterium is able to make use of and hence remove 

 this substance, thus stimulating the yeast to renewed 

 activity. At all events some such action must, we 

 presume, take place, and this curious double fermentative 

 of the two organisms, each benfiting the other, has 

 rightly been termed symbiotic fermentation. 



Thus we have not only in the animal kingdom, as be- 

 tween animals and plants, associations of mutual benefit, 

 but this interaction extends to the vegetable kingdom 

 too ; and here we find colorless plants, called fungi, 

 forming a league with green self-supporting plants, 

 and these often dependent on the intervention of the 

 fungi, as in the case of the micorhizse-bearing trees and 

 shrubs. 



That we are not always able to point out all the advan- 

 tages gained from such symbiosis is due to a lack of 

 knowledge regarding the requirements of some of these 

 loAvly groups of plants, and should stimulate all of us to 

 further research in this field. The facts, and the inter- 

 pretation of these facts, which I have brought before you 

 herein will, I hope, arouse in some of you an interest in 

 these problems of vegetable economics and sociology, 

 and lead you to take some part in this fascinating study 

 of symbiosis. 



Bacteria of School-rooms. — Ruete and Enoch have made 

 an investigation of germs found in school-rooms. A maximum 

 number of over 3,000,000 living germs per ccm., a minimum 

 number of 1500 per ccm. and an average of 268,000 per ccm. 

 of air were found of the 18 species described, but one was found 

 pathogenic for mice, guinea pigs, and rabbits. The quantitative 

 determinations were made by passing a measured amount of 

 air through liquified gelatine (Centralblatt f. Balkt. u Para- 

 siten Runde, XVII 1, 128). 



