EEMAEKS ON TECHNIQUE 19 



Culture Media. 



Besides the usual media (agar, gelatine, bouillon, potato) whose 

 preparation can be found in any bacteriological text-book, the more 

 delicate media containing serum, are especially useful in ophthalmic 

 work ; in fact, many of the organisms with which we have to deal 

 will only grow on these latter. 



Loffler's blood-serum occupies the first place. This is obtained by collecting the 

 fresh blood of sheep, cattle, or horses in clean sterile dishes, and letting it stand till 

 the serum separates off. The serum is then decanted into a clean glass dish, shaken 

 up with chloroform to sterilize it, and again decanted. It is then mixed with 

 one-third its bulk of grape-sugar bouillon, poured into test-tubes (each 5 c.cm.), 

 and on a sloping stage fractionally sterilized at 60 C. half an hour every day for 

 a week. 



Simple coagulation by moist heat at 100 C., as is carried out at many diphtheria 

 research laboratories, cannot be recommended. Many organisms, Staphylo- 

 cocci, and especially those of the diphtheria group, grow very well on this ' cooked ' 

 serum, but others e.g., Pneumococci grow very badly. 



It is important that the serum and this is true for all media in ophthalmic 

 practice should not be too alkaline, especially when we are dealing with the 

 Pneumococcus. The bouillon should therefore be quite neutral, for the serum 

 itself always has a marked alkaline reaction. 



This last particular must be carefully attended to in the preparation of serum 

 agar by the Wertheim formula. This medium is very valuable for growing the 

 'difficult' organisms (Bac. Koch-Weeks, Bac. duplex, Pneumococcus, Gonococcus, 

 etc.), and when properly prepared in the following manner is by far the most 

 useful : 1 per cent, neutral agar is liquefied, and cooled down to 45 to 50 C. in a 

 water-bath ; to this is added one-third to one-fourth its bulk of human serum 

 (ascites, hydrocele, pleuritic, or ovarian cyst fluid), previously sterilized fractionally 

 at 60 C. Immediately after mixing the tubes are sloped ; they must not be further 

 heated, or the serurn would coagulate. It is just this addition of uncoagulated 

 human serum which makes the medium so susceptible. These body fluids vary in 

 alkalinity to no small degree, and when they are very alkaline the agar should be 

 slightly acidified. 



The suitability of sera varies, and is not even constant for one and 

 the same organism. In making important determinations of growth, 

 a trial culture should always be made with Pneumococci or Gonococci. 



The media containing hemoglobin have, in ophthalmic work, a 

 very special importance with regard to the influenza group (Hcemo- 

 phile polebacteria] . On account of its richness in haemoglobin, 

 pigeon's blood is very useful ; it can be rubbed over the surface of the 

 blood-serum with a platinum loop, or added to the bouillon. Human 

 blood can be obtained at operations, or else from one's own purified 

 finger or ear; the first drop is not used, as it may contain skin 

 organisms. 



All blood media so prepared should have their sterility proved by 



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