548 J. 0ESKOV 



following the reflection of the needle in the agar; when the needle 

 and its image meet, contact with the colony has been estabhshed. 

 The point of the needle is now touched with broth in a small loop 

 which is raised so as to encompass it several times, agar is inocu- 

 lated from the loop, and finally the needle is washed in a tube 

 of broth. 



The "harpoon" is sterilized by flaming, and now it only re- 

 mains to examine the area where the colony was previously 

 situated. The bacteria from the colony will be seen to have 

 been scattered somewhat, and we note whether the adjacent 

 colonies are totally intact, both with the low and with the high 

 power of the microscope. In case growth results from the inocu- 

 lation we know that we have obtained a reliable pure culture. 

 Compared with Hort's dry-lens method, the procedure described 

 presents several advantages. Firstly, it is difficult to pour agar 

 over the shdes so as to obtain an even layer, and it takes a long time. 

 Petri dishes with agar are always at hand in any bacteriologic lab- 

 oratory; these should however be freshly poured to avoid the risk 

 of obtaining pure cultures from chance microorganisms from 

 the air which, being overlooked at inoculation, may have formed 

 small colonies. Secondly, we avoid the perforated celluloid 

 plate which is a hindrance to free operation and means a con- 

 siderable hmitation in the possibility of finding conveniently 

 placed microorganisms. While Hort spends several hours on 

 the pure cultivation of a bacterium by his method, I beheve that 

 the total work in my isolation method \\-ill, in most cases, only 

 amount to a fraction of an hour for each single bacterium. 



As has been shown, we are able to trace the growth from the 

 single cell until a small colony has developed. Details can of 

 course only be observed as long as the colonies are small and 

 single-laj'ered ; so soon as the colonies are crowded in several 

 layers, exact examination is of course out of the question. If, 

 for instance, we desire to ascertain whether a morphologically 

 at3T)ical element is viable, and to follow its development, we 

 isolate it as described above and observe its growth at proper 

 intervals. If it is desired to get a su^^'ey of the way in which 

 colony formation proceeds we need only, at proper intervals, 



