SECTION CUTTING. 183 
logical diagnosis. The presence of bacteria in the 
tissues can usually be demonstrated by the simple 
processes of smearing the cut surfaces of tissues on 
clean slides or cover-glasses, and treating the films thus 
obtained by the fixing and staining methods previously 
described. If, for instance, we have to search for 
tubercle bacilli in tuberculous glands it is usually 
sufficient to smear the cut surfaces of the glands on 
a slide, dry, fix by heat, and stain in the same way as 
sputum is stained for the tubercle bacillus. If anthrax 
bacilli were being looked for in the liver or other 
organ, removed post-mortem, the same method of pro- 
cedure would be adopted, except that Gram’s method 
of staining would be used. So also for typhoid bacilli 
in the spleen, where the film would be stained with a 
simple stain such as thionin or Léffler’s methylene blue. 
It seems advisable, however, to give a short general 
account of the processes involved in section cutting, for 
they are by no means difficult, and do not require very 
expensive apparatus. Further, the same methods of 
section cutting are used for investigating the nature of 
tumours, &c., and this is done already by many practi- 
tioners and should be done by still more. 
Slices of organs or tissues which are to be cut have 
first to be fixed. The process of fixation consists essen- 
tially in the application of some agent which brings 
about coagulation of the component proteids with as 
little distortion of the morphological elements as pos- 
sible; if this step were not carried out the subsequent 
processes would be liable to cause alterations in the 
shape, size, and appearance of the cells and fibres. 
There are two chief methods or fixation, that involving 
the use of chemical substances, and that involving the use 
of heat. The processes which are used in fixing the 
