6 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



Many bacteria are multicellular, and their appearance is much altered by 

 drying. The granular appearance of the tubercle bacillus is due to the shrinkage 

 of the contents of the small, almost spherical cells which make up the bacillus, 

 so that unstained gaps appear between them. In this case also the cell wall 

 remains unstained, but retains the dried cells in their original relationship. 



It will thus be seen that three main problems must be solved in the demon- 

 stration of the true morphology of bacteria. Distortion due to drying must 

 be avoided, the masking effect of the strongly staining protoplasm and cell 

 membranes overcome, and those structures demonstrated which, like the cell 

 wall, are difficult to stain. The first is simple and entails merely the avoidance 

 ot drying at all stages of preparation. The second and third present more 

 difficulty. The problem of overcoming the masking effect of the surface 

 structures was solved, as so often happens, by accident. 



B: HYDROLYSIS TECHNIQUES FOR NUCLEAR STAINING 



(13, 15, 16, 19, 24, 30, 32, 40, 41, 44, 46, 48, _so, SI, 5^. 5i, 57) 



The Feulgcn reaction is a microchemical test which depends upon the 

 formation of a purple compound when aldehydes react with Schiff's reagent, 

 A positive Feulgen reaction is given by deoxyribose nucleic acid, after its 

 purine bases have been removed by acid hydrolysis. Ribonucleic acid does 

 not give a positive reaction. The hydrolysis is performed in Normal hydro- 

 chloric acid at a temperature of 60° C, and the subsequent staining with 

 Schift 's reagent reveals the nuclear structures o( bacteria with reasonable 

 clarity. This was one ot the first methods to give a true picture of the bacterial 

 nucleus, and it was later discovered that if the final staining was pertormed 

 with Giemsa's solution, instead of Schiff's reagent, a much clearer picture 

 was obtained. This was the acid-Giemsa stain, which has been the basis of 

 nearly all recent work upon the bacterial nucleus, although the information 

 which it pr(widcs can be verified by other methods. 



The purpose of the preUminary treatment with hydrochloric acid is 

 two-fold. The nucleoproteins of the underlying structures are partially 

 hydrolysed so that the aldehyde group of the associated pentose sugar is 



