104 PRACTICAL BACTERIOLOGY. 



the section is rinsed with distilled water, in order to 

 wash off all superfluous colouring matter, and is then 

 immersed for a few seconds in 1 per cent, acetic acid. 

 After having been taken out of this weak acid, it is 

 again well rinsed in water to remove immediately the 

 last traces of acid. Acetic acid has the power not 

 only of decolourising the tissue, but also the typhoid 

 bacillus ; it is therefore necessary to be very quick, if 

 the colour of the latter is to be retained and that of 

 the former to be only partially abstracted. The sectipn 

 is now transferred in water to the slide, and examined 

 with the microscope. 



If the experiment is successful, the tissue should not 

 be entirely decolourised, but should have a faint .bluish 

 tinge ; moreover the nuclei of the cells should show a 

 distinct blue coloration. If bacteria are present in 

 the section, they are stained a deep violet blue, that is 

 to say, they are of the same colour as the animal tissue, 

 only of a deeper shade. Typhoid bacilli occur gener- 

 ally collected together in small heaps ; section after 

 section of the spleen may be examined in vain to find 

 them, as they occur collected together in nests in this 

 organ. On the other hand they are evenly distributed 

 in the intestine, of which hardly a single section can 

 be cut which does not contain them, provided that 

 they are present in sufficient numbers. This, how- 

 ever, is not always the case, and especially not in 

 every stage of typhoid. If the operator is afraid of 



