24 DE. E. KLEIN. 



powers of the microscope from time to time, without in the least 

 disturbing the growth. Koch, in his paper above quoted, has 

 minutely described all these advantages, and therefore I need 

 not further enter into this part of the subject, as I have no 

 doubt it must be obvious to every one who has the slightest 

 acquaintance with artificial cultivations of bacteria. 



If you have sown in this manner a particular organism 

 well known to you, it is of course easily ascertained on micro- 

 scopic examination immediately after, whether the same is 

 present in any part of the line you have drawn over the gela- 

 tine drop in the above glass-cell specimen with your needle or 

 capillary tube. Thus, inoculating the gelatine drop with the 

 Bacillus anthracis or with its spores, or the spores of hay 

 bacillus, with sarcina, with torulae, with Micrococcus pro- 

 digiosus, &c., you can at once find these seeds in the streak 

 you have drawn on the gelatine drop ; according to the number 

 of seeds present in the material to be sown there will be more 

 or less numerous seed in that streak. If in addition to this 

 you have sown only one species of those named any accidental 

 contamination will soon be detected under the microscope in 

 the gelatine drop, say after a day or two or longer. 



But supposing you are sowing a material of which you do 

 not know whether it contains any organism, or, if so, what kind 

 of organism, the case is altogether different, and 'the value of 

 this method is not obvious ; on the contrary, may lead to serious 

 errors ; in this way : the inoculation of the solidified gelatine 

 nourishing material, Avhether in my glass- cell specimens or 

 after Koch's plan, on glass slides or flat dishes, must take 

 place in the air, and there is no means to prevent contamina- 

 tion with air organisms. Under ordinary circumstances and 

 working quickly the chances of such contamination are not very 

 great, but are, nevertheless, objectionable. Now, supposing 

 that you inoculate your gelatine in several specimens with the 

 material to be tested for organisms, you may find after a day or 

 two or more of incubation that in one or more of the specimens 

 in the streak you have drawn there is no growth whatever of 

 any organism, but outside it at other points an organism or 



