ESTIMATION OF THE OPSONIC POWER OF THE BLOOD 2OQ 



follows : The cultures should in all cases where practicable 

 be prepared from the organisms isolated from the patient 

 himself. "Stock" vaccines may do good in some cases, 

 especially, perhaps, in staphylococcic diseases; but in 

 diseases due to streptococci, B, coli, etc., they are not nearly 

 so likely to succeed as vaccines specially prepared : these 

 organisms differ slightly in different cultures, and a vaccine 

 prepared from one variety may have little action on another. 

 The culture should be made on agar (or blood-agar in the 

 case of gonococci, etc.), and should be as young- as possible. 

 To each culture-tube about 2 to 5 c.c. of sterile normal saline 

 solution are added, and the bacteria scraped off by means of 

 a platinum needle and the tube gently shaken, so that the 

 organisms are emulsified. The number of bacteria in this 

 emulsion must next be counted. Wright's method is usually 

 employed, and is carried out by mixing the bacterial sus- 

 pension with blood in known proportions, making films, and 

 counting the red corpuscles and bacteria in the same field 

 of the microscope, so as to obtain the relative proportions of 

 the two. The number of- red corpuscles per cubic millimetre 

 is known (or can be counted), and from that the number 

 of organisms can be calculated. Proceed as follows : 

 Take an opsonin pipette, and draw up one volume of blood 

 from a healthy person, then a bubble of air, then one volume 

 of citrate solution (p. 202), then one volume of the emulsion. 

 Mix them together on a slide, make films on two cover- 

 glasses, dry, and stain by Jenner's method. Proceed to count 

 the red corpuscles and bacteria on several fields of the micro- 

 scope : this will be easier if you rule four ink lines enclosing 

 a square on the lower lens of your eye-piece, and count the 

 objects lying therein. When you have done this, move the 

 slide so as to get a fresh field, and count again. Do this 

 many times, add the totals of the corpuscles and of the bac- 

 teria, and calculate the ratio between the two. (Thus in one 

 case the red corpuscles on the various fields were 18, 15, 20, 

 21, 14, 17, 10, and 15; and the bacteria 37, 26, 31, 40, 25, 30, 

 32, 36 : the totals were 130 and 257, or, roughly, i to 2.) 

 The calculation of the number of bacteria per cubic milli- 

 metre is then easy, and that multiplied by 1,000 gives 

 the number per c.c. 



Next the emulsion has to be sterilized by heat. It is placed 



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