1886.] 



MICROSCOPICAL JOURNAL. 



125 



of the Bacillus subtilis. This re- 

 sembles very much the B . anthracis^ 

 so much so in fact that Biichner an- 

 nounced at one time that he had suc- 

 ceeded in converting the deadly B . 

 ant/wacis into the harmless B. sub- 

 tilis. His experiments are not con- 

 sidered reliable, and his conclusions 

 ai"e contradicted by the spore germi- 

 nation of the tvs^o forms. The 

 Bacillus subtilis produces spores 

 which resist boiling, and this fact is 

 the key to the discussion on spon- 

 taneous generation w^hich raged so 

 violently some twenty years ago. In 

 sterilizing other infusions this bacillus 

 is often found if the boiling has not 

 been thorough. 



A simple method of isolating 

 various forms of bacteria is by the 

 use of gelatin plates. The gelatin 

 should be neutral or slightly alkaline- 

 as an acid reaction is unfavorable to 

 bacterial growth. If about y\j c.c. 

 of Potomac water be added to some 

 liquid gelatin and thoroughly dis- 

 tributed in it and the gelatin poured 

 upon a sterilized plate, colonies of 

 bacteria will begin to appear in a few 

 days. Plates were shown containing 

 several colonies from water, saliva, 

 etc. Insects gaining access to the 

 plates by accident, have left behind 

 them several curious forms of bacteria . 

 Sterilized potato is a good medium 

 for the culture of bacteria. To ster- 

 ilize a potato wash it thoroughly and 



scrub it with a brush. Place it in a 

 yip per cent, solution of corrosive sub- 

 limate for half an hour ; then suspend 

 it over a steam bath by means of wire 

 gauze for another half hour, then 

 transfer it to a glass stand under a 

 bell-glass and cut it, under the bell- 

 glass, with a sterilized knife. Another 

 culture medium is agar-agar or Jap- 

 anese isinglass which is not liquified 

 by certain bacteria as is gelatin, and 

 lasts much longer. Several cultures 

 on this medium in tubes were shown. 

 The best tubes and cotton plugs are 

 sterilized by steaming them on four 

 or five successive days at least five 

 minutes. 



To examine any of these cultures 

 microscopically it is only necessary 

 to transfer a minute quantity of the 

 culture or colony with a flamed plat- 

 inum wire to a cover-glass either with 

 or w^ithout a drop of sterile water. 

 Pass the cover-glass, with the dried 

 film on it, two or three times through 

 the flame of a Bunsen burner, invert 

 it over a dish containing an aqueous 

 solution of some aniline such as 

 methyl violet or methylene blue and 

 allow it to remain until stained. 

 Wash oft' the excess of stain and 

 mount. In using the Abbe condenser 

 with stained preparations remove the 

 diaphragm ; in examining unstained 

 or living specimens use the smallest 

 possible diaphragm opening compat- 

 ible with a sufficient amount of light. 



Key to the Desmidieae. 



BY DR. A. C. STOKES. 



\_Co7itiniied from i>age 114.^ 



17. CoSMARIUM. 



§ End view without central inflations (i). 

 § End view with central inflations (2). 

 I. Cytioderm smooth or punctate (a). 

 I. " more or less verrucose or granular (y) 



spinous i^g) . 



2. Cytioderm smooth or punctate (/^). 



2. " more or less verrucose or granular (/) 



a. Chlorophyll diffused {b) . 



a. Chlorophyll concentrated in i or more nuclei (e) . 



