158 



Journal of Applied Microscopy. 



The forceps may be of any form, 

 but a flne-pointed instrument is well 

 adapted for tlie handling of the thin 

 cover-glasses. Inasmuch as there are 

 certain drawbacks to the use of the ordi- 

 nary forceps, I have for several years 

 employed a modification better adapted 

 for the object in view. This cover-glass 

 forceps of mine is reproduced in Fig. 1. 



Fig:. 1. 



The lower blade of the forceps is flat 

 and has a wide end and sharp edge. It 

 can therefore pick up cover-glasses read- 

 ily from the table or from any flat sur- 

 face. The upper blade of the forceps 

 ends in a fine point and is bent down- 

 ward so that an appreciable space re- 

 mains between the two blades when the 

 points are brought together. In the ordi- 

 nary forceps, during staining, the liquid 

 tends to creep up along the capillary 

 space between the blades, and as a result 

 the hands of the student display more 

 color than does his preparation. This 

 capillarity is done away with in this in- 

 strument, especially if the cover-glass is 

 held at the very edge. The pressure ex- 

 erted must be light. The advantages 

 mentioned are such as will commend the 

 forceps to those who have occasion to 

 frequently handle cover-glasses. The 

 above instrument can also be obtained 

 provided with a clamp as in the case of 

 Ehrlich's forceps. 



The platinum wire should be of number 

 21 gauge and about two inches long. It is 

 fused into the end of a glass rod or tube 

 six or seven inches in length. 



ISOLATION OF BACTERIA. 



A great variety of bacteria, moulds, 

 and yeasts can be obtained by the be- 

 ginner from the air. It matters not 

 where he may live, the air will always 

 supply a large number of species. The 

 following simple procedure will enable 

 anyone to grow these bacteria from 

 the air, and thus obtain a variety of 

 organisms suitable for examination in 

 the living condition and for staining 

 purposes. 



Place two or three sound potatoes and 

 a knife in a vessel of water and boil for 

 twenty minutes. Then pour out the wa- 

 ter, and as soon as the potatoes are fair- 

 ly cool, cut them in two with the knife, 

 which has been sterilized by boiling. Ut- 

 most care must be taken not to touch 

 the blade of the knife or the surface of 

 the cut cooked potato. Each half is 

 placed on a piece of paper with the cut 



surface uppermost. The halved potatoes 

 can be exposed uncovered for a variable 

 length of time to the air, say five, ten, 

 fifteen, or thirty minutes. They should 

 be carefully covered with a clean glass 

 tumbler, without touching the potato. 

 After thirty-six to forty-eight hours, the 

 potato will usually show one or more 

 pinhead growths. These increase rapidly 

 in size in another day or two. If a well 

 cooked potato is placed under cover im- 

 mediately after halving it, and after a 

 day or two shows no growth on the sur- 

 face, it will indicate clearly that the 

 operator is doing the work as it should 

 be done, that is, under strictly sterile 

 conditions. The growths, therefore, that 

 develop upon the other potatoes which 

 have been exposed to air are due to or- 

 ganisms which, floating about in the air, 

 have dropped down onto the potato and 

 have found this to be a good soil to grow 

 upon. 



When flrst seen, the growth will be 

 pin-point or pinhead in size. Inasmuch 

 as it results from a single germ which 

 has dropped down onto the potato, it fol- 

 lows that this growth contains only that 

 particular organism. The single organ- 

 ism rapidly multiplies and gives rise to 

 its own kind. This pinhead growth, 

 known as a colony, since it is made up 

 of only one kind, is a pure culture of 

 that organism. 



EXAMINATION OF LIVING BACTERIA. 



When the colonies have developed on 

 the potatoes, they should be examined 

 and studied carefully in the living con- 

 dition. To do this, a little of the growth 

 is picked up on the end of the platinum 

 wire, which first, however, has been 

 heated in a fiame and allowed to cool. 

 That is to say, the platinum wire must 

 first be sterilized. 



The wire, with a little of the growth, 

 is then touched several times to a drop 

 of water on a glass slide. The drop of 

 water should as a result show a visible 

 cloudiness. It is then covered with a 

 cover-glass and examined under the 

 microscope. 



The two-thirds-inch objective will show 

 up some fine granules in the water, but 

 their form and nature cannot be made 

 out. To ascertain this, examine with 

 the one-eighth-inch objective, and later 

 with the one-twelfth-inch oil-immersion 

 objective if such is at hand. 



The true nature of the growth will now 

 be apparent. As a rule, the organisna 

 under examination will have the form of 

 a rod. It may be actively motile, mov- 

 ing rapidly from place to place, or it may 

 show only a gentle swaying motion and 

 remain in one place (Brownian motion). 

 The rod-shaped organism is designated 

 as a bacillus. The greatest variety of 



