EEMAEKS ON TECHNIQUE 9 



and v. Lingelsheim advises that the alcohol should be only used for 

 thirty seconds. It certainly should not be left on too long, for many 

 positive organisms will in time lose their colour. With the original 

 Gram solution, which stained slowly and less intensely, organisms 

 were often called negative which we now know to be positive (see 

 ' Gonococcus '). Only those organisms should be called negative 

 which, after the technique recommended, completely lose their blue 

 colour. The Jadassohn modification gives so intense a stain that the 

 alcohol can be used as long as the colour is obviously being washed 

 out. A good and diagnostic contrast is thus obtained. 



The same technique should always be used, and in ssientific work, 

 in questions of this kind, it is best to state how the Gram stain was 

 applied. 



The organisms of interest in ophthalmology which stain positive are : 



Most of the Sarcince ; 



Staphy locoed, Streptococci, Pneumococci ; 



Bacilli of the Diphtheria and Subtilis groups ; 



Bac. perfringens (Chaillous) ; 



Aspergillus fumigatus, Streptothrix, and Actinomyces. 



Staining negative are : 



Bacilli of Koch- Weeks and Pfeiffer (L. Miiller, influenza) ; 



Diplobacillus of Morax-Axenfeld and Petit ; 



The Coli group ; 



Gonococcus, Meningococcus, Micr. catarrhalis ; 



Bac. pyocyaneus ; 



Group of Friedldnder's pneumobacillus. 



Staining- of Sections. 



For the examination of bacteria in sections hardening in formol is 

 best. Sublimate, too, can be used if it be thoroughly removed after- 

 wards by iodine ; Zenker's fluid also, if only used for a short time 

 and then thoroughly washed away. Similarly, Miiller's fluid, if for 

 a still shorter time, and still more thoroughly washed away. These 

 latter are not so good. 



For sections of the whole eye celloidin embedding is better than 

 paraffin; small pieces of a tissue, however, stain very well after 

 paraffin. 



For all Gram-positive organisms (e.g., Pneumococci in sections of 

 an ulcus serpens) the most suitable stain is Weigert's modification of 

 Gram, which stains fibrin also. 



