TEXT-BOOK OF BACTERIOLOGY. 49 



swells and dissolves, may be washed from the cover-glass, and often 

 causes deposits under the influence of the staining solution, which 

 spoil the preparation. 



Albuminous fluids may be fixed on cover-glasses, as recom- 

 mended by Ehrlich, by exposing the glasses to a heat of 120° C. 

 for about twenty minutes, or, what is much more convenient and 

 equally efficacious, draw them, as recommended by Koch, three 

 times, at a moderate speed, through the flame of a Bunsen burner, 

 with the preparation on the upper surface, to avoid its coming in- 

 to direct contact with the flame. 



When cautiously heated in this manner, the forms of the cells, 

 bacteria, etc., do not alter in the least, nor do they lose any of their 

 capacity for absorbing color; the albumin, however, passes into an 

 insoluble state, in which condition it remains unchanged under the 

 further manipulation of the cover-glass in the process of staining. 



A few precautions must not be neglected. The preparation must 

 be completely air-dried before it enters the flame; otherwise the 

 albuminous matter coagulates under the influence of a high tem- 

 perature, instead of becoming homogeneous. Again, the heating 

 process must not be carried too far. Many bacteria — for instance, 

 the anthrax bacilli — are extremely sensitive to an excess of hea tins'; 

 they change their form, break up into separate granules, or swell 

 up like bubbles, become surrounded with a sort of halo, and lose 

 their ability to stain. 



It is generally sufficient if we draw the glass tliree times through 

 the full flame of a Bunsen burner, at about the same rate as tlie 

 movement with which we wave a handkerchief in salutation to a 

 person at a distance. It may be that some wave it more rapidly 

 than others, but we can take the average speed. If instead of a 

 Bunsen burner a spirit-lamp is employed, the time must, naturallj', 

 be correspondingly lengthened. 



This procedure is necessary only for preparations containing 

 albumin. Yet as tlie heating above described is not deleterious for 

 other objects, and as it cannot always be known whether coagula- 

 ble matter is present or not, we habitually prepare all cover-glasses 

 for staining in this manner. 



The manner of removing bacteria from a liquid or solid nour- 

 ishing medium to a cover-glass has been described. To examine 

 blood and tissue fluids from an animal just dissected the following 

 procedure is necessary. 



Either take up a drop of blood with the bent wire previously 

 heated, and put it on the cover-glass, or press a small piece of any 

 organ gently against the glass, rubbing it over the surface and so 

 4 



