METHODS OF INVESTIGATING BACTEBIA. 779 



better "by laying a second coyer glass on the top of the 

 first, so that the drop is spread out, and the layer of 

 fluid extends to the border of the cover glass ; these 

 glasses are then slid asunder, and thus we obtain two 

 thinly-spread layers ; these layers dry in a few minutes. 

 If now the cover glass is at once brought into con- 

 tact with the staining solution the layer again becomes 

 detached, and is washed away; hence the organisms 

 must first be fixed on the glass as far as possible. 

 This can be done either by prolonged immersion of the 

 glasses in absolute alcohol, or by exposing them for a 

 short time to a temperature of from 110 to 130 C. 

 (for two to ten minutes), but the exact degree of heat 

 differs somewhat in the case of different objects, and 

 must be ascertained by experiment. This heating can 

 be conveniently and sufficiently done by passing the 

 cover glass two or three times slowly (" about as quickly 

 as we cut bread ") through the flame of a Bunsen burner 

 or a spirit lamp. After this treatment the organisms 

 adhere so firmly to the glasses that these can be kept 

 for a long time in watery fluids without any bad result. 



The cover glass being prepared in this way a drop of 

 one of the staining solutions mentioned below is placed on 

 it ; it usually suffices to allow the solution to act for from 

 fifteen to twenty minutes ; if we wish to prolong the action 

 it is advisable to float the cover glasses on the staining 

 material contained in a flat vessel. The cover glass is 

 then seized with forceps, freed from the stain by filter 

 paper, washed in distilled water, or at times in very 

 dilute acetic acid (5 to 10 drops to 100 com. of water), 

 and then placed on the slide with a drop of water, or 

 else dried and mounted in oil of cloves or Canada 

 balsam. 



Organs must in the first instance be hardened in Treatment of 

 absolute alcohol for some time (several days) ; in doing sec 

 this plenty of alcohol must be used, and it is well to cut 

 the organs into small pieces. A number of fine sections 

 are then made, if possible by means of a microtome, and 

 are placed in the first instance in absolute alcohol, and 

 from thence transferred to the staining solution. The 



