60 TEXT-BOOK OP BACTERIOLOGY. 



It supplies US with durable preparations which permit of com- 

 parative examination. 



It is staining alone that gives us an immediate insight into the 

 micro-organic life that exists within the tissues, and it is double 

 staining that enables us to differentiate between tissue and bacteria 

 with such extraordinary clearness and precision. 



By means of staining — that is to say, by means of the peculiar re- 

 lations existing between particular stains and particular species of 

 bacteria — attention has been directed to the special importance of 

 many kinds of micro-organisms, and a successful staining has thus 

 been the first step on the way to important discoveries. 



Coloring is an invaluable aid in the hands of those who know 

 how to employ it, but it is an art that must be studied, and- the 

 great number of the so-called " faults of investigation " — defective 

 observations of different kinds — show that here also apprentice- 

 ship must precede mastership. 



The most common of these faults of investigation are as follows. 

 A part of them arise from an insufficient preparation of the object. 



Glass covers are heated before they are completely air-dry, or 

 they are exposed too long to the action of high temperature. This 

 causes the formation of those peculiar alterations of shape which 

 have already been mentioned. The bacteria swell up, or they col- 

 lapse, or they become surrounded by a halo, and quite lose their 

 characteristic appearance. 



There is another fault, too, referable to an insufficient previous 

 treatment of the preparations. If portions of organs are left too 

 long before being put into alcohol, they begin to putrefy — i.e., the 

 septic bacteria gain access to them. If these objects be hardened 

 and the sections made from them be colored, these foreign micro- 

 organisms are of course stained with the rest, and thus give rise 

 to all sorts of deceptions. 



To avoid these, put the portions of tissue, as fresh as possible, 

 into alcohol, but besides this, be particular to notice the distribution 

 of the bacteria within the section. 



The septic bacteria, of course, penetrate the organs from with- 

 out; 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 them. 



Another error proceeds from the fact that many of our staining 

 solutions, especially hiematoxylon and carmine, but also the anilin 

 colors and even distilled water, are often enough the home of 

 numerous bacteria, which find there a field for their development. 

 When staining our objects, these micro-organisms are deposited 



