166 AIDS TO BACTERIOLOGY 



set being incubated at 25 C., the other at 15 C. In a 

 pure brewery yeast no ascospores will be detected under 

 thirty hours and seventy-two hours respectively. 



Hanson found that the formation of spores takes place 

 slowly at low temperatures, more rapidly as the tempera- 

 ture is raised to a certain point; when this point is passed 

 their development is again retarded, until finally a 

 temperature is reached at which it ceases altogether. 

 After a time, which varies with the species, roundish 

 plasma particles appear in the cells. These are the first 

 indications of spores. They become surrounded by a 

 wall, seen more or less distinctly in different species. 

 The spores may expand to such an extent that the pres- 

 sure which they exert on each other whilst still enclosed 

 in the mother cell develops the so-called partition walls. 

 Later complete union of the walls may take place, so 

 that a true partition wall results; the cell then becomes 

 a compound cell, divided into several chambers. During 

 germination the spores swell, the wall of the mother cell, 

 originally thick and elastic, stretches thinner, finally 

 ruptures, and then remains as a loose shrivelled skin, 

 partially covering the spores, or else dissolves. 



3. The Formation of Films. With the pure cultivation, 

 drop cultures are made into 4-ounce flasks, half filled 

 with sterile wort, and protected from falling particles 

 by a well-fitting cap. The films first appear as small 

 opaque points, which gradually increase in size and then 

 run together, forming irregular floating patches. As soon 

 as the film becomes apparent to the naked eye it is 

 examined. The film at length overspreads the whole 

 surface of the liquid, and becomes adherent to the walls 

 of the flask. Perfect rest of the liquid is a very necessary 

 condition for the formation of films. 



Hansen's Pure Culture Method. Bdttcher's moist chamber 

 consists of a short glass cylinder or ring, cemented to 

 the upper surface of a glass slip. A cover-glass rests on 

 top of the ring. A small drop of water is placed at the 

 bottom of the chamber. A mixture of yeast growth 

 and sterile water is mixed with a suitable amount of 

 wort gelatin, which has been previously liquefied at 30 

 to 35 C. A very small quantity of the mixture is spread 

 in a thin layer on the sterile cover-glass and left under 

 a sterile bell -jar to set. The edge of the ring of the 



