BACTERIOLOGICAL TECHNIQUE 39 



3. The slide must be carefully heated over the flame, 'not 

 cooked, 1 until the section is dry, when it is allowed to cool and 

 mounted in xylol balsam. 



Contrast stains by this method are of little use, as the tissue cells 

 are too much altered by the heating. Professor Gunther recommends 

 the 'Dry Method of Unna' as the only way to obtain permanent 

 specimens of tubercle bacilli in sections. 



XLVII. NECESSARY PRECAUTIONS IN THE MANIPU- 

 LATION AND STAINING OF SECTIONS. 



1. When staining sections, never do a number at once until you 

 have tested the correctness of your method in a few first. 



2. In the enumeration of the various staining methods precise 

 directions as to time, etc., have been given ; it is well, however, to 

 remember that these directions are for uniform preparations of the 

 stains, solutions, etc. 



3. By staining, the difference in length of bacteria, however slight, 

 is demonstrated, also the extremely characteristic shape of some 

 species. 



4. By staining, an insight is gained into micro-organismal life 

 existing in the tissues, while double staining enables the bacteria to 

 be distinguished from the tissues with remarkable precision. It is an 

 art requiring great care and study, invaluable in the hands of those 

 who know how to employ it. 



XLVIII. THE FOLLOWING ARE THE MOST COMMON 

 STAINING FAULTS. 



1. Portions of organs left too long before being put in alcohol 

 commence to putrefy, i.e., putrefactive bacteria and fungi gain access, 

 and in staining sections from such a specimen, for a definite organism, 

 the putrefactive bacteria are also stained, and such being the case, 

 particular attention must be given to the distribution of the bacteria 

 throughout the section, as putrefactive bacteria penetrates the organ 

 or piece of tissue from without, their numbers are therefore found to 

 diminish in proportion to the distance from the outside surface, while 

 the inner portions are usually quite free from putrefactive bacteria. 



2. Many staining solutions, i.e., carmine, hsemotoxilin even 

 distilled water, and some of the anilin colours often contain bacteria. 



3. Faulty staining is liable to occur by the Gram method, when 



