280 XXI. BACTERIA YEAST. 



of the sharply-pointed colour pencils (Faber's) mentioned in the 

 Introduction, or with a writing diamond. It is then easy later on 

 to replace the object-slide thus marked in exactly the same 

 position. 1 If the food-materials of the drop are approaching 

 exhaustion the vegetative segmentation or bipartition is arrested, 

 and the endogenous spore -formation at once begins. After the 

 lapse of from six to eight hours there can be seen in the threads, 

 at thereabouts equal distances, elliptic, strongly refractive spores 

 (Fig. 104 C). The threads appear otherwise empty; only the 

 colourless sheaths unite the spores. At various places in the 

 preparation, one is certain to find spores still in course of forma- 

 tion. They appear in the form of collections of more refractive 

 material, situated most usually towards the middle of the rodlet. 

 The aggregation becomes continually more marked, while the 

 rodlet becomes emptied, and at last the formation of the spore 

 is complete. If the culture is allowed to continue some hours 

 longer, the sheaths of the rodlets will have become indistinct, and 

 after the lapse of about a day the spores appear free, and sunk 

 to the bottom of the drop. Under unfavourable cultural conditions, 

 as, e.g., with too large a proportion of sugar in the culture fluid, 

 there arise irregular swellings and abnormal changes of form in 

 the cells (involution forms). 



The spores germinate very easily if they are transferred 

 to fresh nutrient fluid ; more slowly at the temperature of the 

 room, quicker at 30 C. ( = 86 F.). It is best to boil them for 

 five minutes, and cool them slowly. Then in about two to 

 three hours we can see the commencement of germination. The 

 spore-membrane is opened on one side, the minute germ begins 

 to protrude here, and elongates gradually into a rodlet ; so that 

 the long axis of the sporeling is at right angles to the long axis of 

 the spore. Its hinder end remains inserted in the spore-case. 

 About twelve hours elapse before the rodlet divides for the first 



*For the purpose of keeping a particular spot under observation for 

 several successive days, i.e., without removal from the stage of the micro- 

 scope, one end of a few strands of loose wick can be inserted between the 

 layers of the pasteboard, while the other end can dip into a vessel of distilled 

 water. The water sucked up by the wick will keep the pasteboard moist. 

 Opticians also construct mechanical stages to microscopes, by means of 

 which a movement in two rectangular directions is possible, an apparatus 

 which, with its appropriate "finder" not merely facilitates replacing an 

 object in any exactly-desired position, but also enables a rapid survey of the 

 whole of a large surface to be made. [En.] 



