316 METHODS OF IDENTIFICATION AND STUDY 



respectively. Other experimental animals e. g., the 

 white rat, guinea-pig, and rabbit should next be 

 tested in a similar manner. 



7. If the inoculated mice are unaffected, test the 

 action of the organism in question upon white rats, 

 guinea-pigs, rabbits, etc. 



Minimal Lethal Dose (m. I. d.); If the purpose of the 

 inoculation is to determine the minimal lethal dose, a 

 slightly different procedure must be followed. For this 

 and other exact experiments a special platinum loop is 

 manufactured, some 2.5 mm. by 0.75 mm., with parallel 

 sides, and calibrated by careful weighing, to determine 

 approximately the amount of moist bacterial growth 

 the loop will hold when filled. 



1. The cultivation must be prepared on a solid 

 medium of the optimum reaction, incubated at the 

 optimum temperature, and injected at the period of 

 greatest activity and vigour, of the particular organism 

 it is desired to test. 



2. Arrange four sterile capsules in a row and label 

 them I, II, III, and IV. Into the first deliver 10 c.c. 

 sterile bouillon by means of a sterile graduated pipette ; 

 and into each of the remaining three, 9.9 c.c. 



3. Remove one loopful of the bacterial growth from 

 the surface of the medium in the culture tube, observ- 

 ing the usual precautions against contamination, and 

 emulsify it evenly with the bouillon in the first capsule. 

 Each cubic centimetre of the emulsion will now con- 

 tain one-tenth of the organisms contained in the 

 original loopful (written shortly o.i loop). 



4. Remove o.i c.c. of the emulsion in the first cap- 

 sule by means of a sterile graduated pipette and 

 transfer it to the second capsule and mix thoroughly. 

 Drop the infected pipette into a jar of lysol solution. 

 This makes up the bulk of the fluid in the second cap- 

 sule to 10 c.c., and therefore every cubic centimetre 

 of bouillon in capsule II contains o.ooi loop. 



