ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
401 
This arrangement answers very well for a short time, but if the 
cultivations require to be supplied with air for a long time an automatic 
arrangement becomes necessary. In fig. 58 such an arrangement is given. 
It consists of a flask D, closed by a triply-perforated stopper ; into this 
water slowly and continuously runs through the tube g and drives 
Fig. 58. 
through h the air in E to the culture through the tube i. When, how- 
ever, the vessel D gets so full that the water rises as far as the level of 
the letter h, then the siphon action of k' comes into play and D is emptied 
in a few minutes. Air is sucked in through l to h , and when D is empty 
the water running through g goes on driving the air through In to E. 
As a matter of course, the aerating apparatus is adapted not only for 
fermentation cultivations, but for any kind of culture. 
Plate-making.* — Dr. L. Heydenreich, after pointing out that he 
was the first to introduce the double capsule, though Petri got the credit 
of it, says that when several (6-10) have been filled with the necessary 
quantity of gelatin or agar they are placed on a Koch’s levelling tripod, 
the plate of which is made of metal instead of glass. On the top of 
this is placed a flat pan filled with ice, a procedure which materially 
shortens the time required for setting the plates. 
The special advantages of a metal plate for the purpose alluded to 
are obvious, but a perfect plane sheet of brass sufficiently thick not to 
bend is somewhat costly. A thin sheet of metal backed with wood, 
however, answers the purpose quite well. 
2 E 
1893. 
* Zeitschr. f. wiss. Mikr., ix. (1893) pp. 306-9 (1 fig.)- 
