20 BACTERIOLOGY OF THE EYE 



twenty-four hours in the incubator, for they are often contaminated by 

 Bacteria, especially if a finger has been squeezed to assist in getting a 

 drop of blood. In many "cases it is better to mix the blood with the 

 agar at 40 C. before the tubes solidify, and thus obtain an equal 

 diffusion throughout the medium. The changes in the blood pig- 

 ments and the haemolysis, which have been emphasized by Neisser, 

 Schottmuller, and others, can thus be better observed, especially on 

 plates, than when the blood is spread on the surface. 



Cultures. 



In proceeding to carry out by cultures an examination of the Bacteria 

 on the surface of a healthy or diseased eye, the material obtained 

 should be rubbed, first on a good peptone or glycerine agar, then on 

 Loffier's serum, then on serum agar, and finally on a haemoglobin 

 medium. Thus we have various possibilities in growth before us. 

 And as the cultures become scantier as we pass on to the more 

 susceptible media, we hope to find on them isolated colonies, from 

 which pure cultures can readily be made. 



In many cases, naturally, a good result is obtained with the simple 

 media ; but it is always advisable to take a few serum- tubes as well 

 as the simple agar one, and from the very first to use various media. 



The variety of culture-tubes used, and the number on which the 

 material is stroked out, should be governed, whenever possible, by 

 what is seen in the smear preparation. When the smear shows 

 numerous organisms, several tubes or plates (Petri's) should be made 

 originally, and only a small amount of secretion should be carried 

 over from one tube to the next. When bacilli of the diphtheria group 

 occur in the smear preparation alongside of ordinary cocci, the 

 primary tube used should be agar, and the secondary one or two blood- 

 serum, on which the bacilli in question may be isolated. The same is 

 the case in dealing with the diplobacillary group : several questions 

 will be decided at once by the particular medium used e.g., if Diplo- 

 bacilli grow on agar they are Petit's type, if not Morax-Axenfeld's. The 

 preference of different organisms for different media greatly facilitates 

 their isolation for example, a coccus may grow well on the agar-tubes, 

 while a bacillus admixed may grow better on blood-serum. This is 

 especially evident in the case of the delicate organisms and the media 

 already mentioned. 



In many cases it is advisable to try anaerobic cultivation, especially 

 when determining some uncertain etiological relationship, or in deal- 



