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 Loffler'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 



