1885.] 



MICROSCOPICAL JOURNAL. 



83 



nal mixture which were capable of 

 multiplyino^ in the nutritive gehitin at 

 the temperature of 7o°-8o° F. These 

 pure cultures are represented by mi- 

 nute colonies, which will soon invade 

 one another's territory. To study the 

 differential characters of the various 

 microbes thus isolated, their mor- 

 phology and biology, larger cultures 

 are prepared in the following man- 

 ner : A sterilized needle melted into 

 a piece of glass tubing, to serve as a 

 handle, is made to pierce a given col- 

 ony carefully singled out under a dis- 

 secting microscojje, and then intro- 

 duced into a culture-medium con- 

 tained in these culture-tubes which 

 have been devised by Dr. Salmon 

 and described in the first annual re- 

 port of the bureau, 18S4. These 

 tubes are used exclusively by us for 

 these cultures. The test-tube plugged 

 with cotton which Koch employs 

 seems poorly adapted for the purpose. 

 The media at present employed for 

 the cultivation of pathogenic forms 

 in tubes may be roughly classed as 

 solid and liquid. Nutritive gelatin 

 has been employed quite extensively 

 of late, no doubt on account of its use 

 in the culture and diagnosis of the 

 ' comma-bacillus.' We have here a 

 number of tubes which illustrate very 

 well the microscopic appearances of 

 different bacteria. The gelatin is 

 liquefied by most of them, but the 

 manner and the progress of liquefac- 

 tion present interesting features. 

 Micrococci which we could not dis- 

 tinguish satisfactorily under the mi- 

 croscope are here shown to grow very 

 differently. Another valuable me- 

 dium introduced /by Koch when 

 cultivating tubercle-bacilli is blood- 

 serum. We have here a series of cul- 

 tures, in this medium, of different 

 forms of micrococci, and each growth 

 presents peculiarities of its own. Sev- 

 eral have the power of liquefying 

 the serum, while the rest limit their 

 growth to the surface, the growth in 

 the track of the needle remaining 

 nearly stationary. These growths 

 on potato are interesting, inasmuch 



as they show that certain pathogenic 

 bacteria may multiply on vegetable 

 substrata, besides furnishing us with 

 additional meai^ of distinguishing 

 diflerent bacteria with the naked eye. 

 Both cultures are micrococci, yet one 

 forms a reddish growth, the other a 

 whitish one. This color, moreover, 

 is not appreciable in any of the pre- 

 viously-mentioned media. 



Various liquid media have been 

 employed in our work, consisting 

 chiefly of decoctions and infusions of 

 lean meat. Sterilized milk offers some 

 points of interest. Certain bacteria 

 will cause speedy coagulation ; others 

 will multiply without producing any 

 perceptible change in the appearance 

 of the milk. Still others may change 

 the appearance and color entirely 

 without inducing coagulation. 



However much may have been 

 said against the use of liquid cultures, 

 we must admit that in general they 

 cannot be dispensed with. They are 

 essential in microscopic work ; they 

 ofter a convenient medium for inocu- 

 lation experiments on animals, for 

 testing all important biological ques- 

 tions such as the influence of heat, 

 disinfectants, etc., and for studying 

 the attenuation of virus. 



The method of plate-culture was 

 first introduced by Koch in the bio- 

 logical analysis of drinking-water. 

 His object was to determine the num- 

 ber and kind of bacteria contained in 

 a given quantity of water. It is evi- 

 dent that in making this application 

 of the method, the scrupulous care 

 necessary in quantitative experiments 

 must be observed, while in the iso- 

 lation of bacteria from a mixture we 

 need not dread the occasional lodg- 

 ment of an aerial germ on our plates 

 as our results are to be qualitative 

 rather than quantitative. Accidental 

 contaminations are usually spores of 

 fungi and isolated colonies of bacteria 

 readily distinguished from the rest. 

 In the same way earth has been sub- 

 jected to analysis with reference to 

 the number and kind of bacteria which 

 it contains. 



