544 



J. 0RSKOV 



been centered, the area is noted by means of the mutual rela- 

 tion of the regular scale and the vernier attached to the mechani- 

 cal stage, and one should now be able to focus exactly in the 

 same place again. At this point there is however a great diffi- 

 culty to be overcome, as the least inaccuracy in the re-adjust- 

 ment may have the effect of causing the selected organism to 

 vanish from the field of vision, others being substituted, and, 



Fig. 2 



even though the most painful care be taken, the same fatal 

 accident may happen o\\dng to quite negUgible displacements 

 of the scales, which it is often quite impossible to control. 



In order to be able to find a particular bacterium again, I 

 have proceeded in the following manner: Prior to placing the 

 agar plate on the slide, a complex of fine lines are by means of 

 a diamond scratched criss-cross, preferably on the lower surface 

 of the shde, over the area to be covered by the agar (cf. fig. 2, 

 above). The lines will become less fraj^ed in the glass if the 



