MINIMAL LETHAL DOSE 319 



1. Filter the cultivation through a porcelain filter 

 candle (Berkfeld) into a sterile filter flask, arranging 

 the apparatus as in the accompanying figure (Fig. 160). 



2. Inoculate mice, rats, guinea-pigs, and rabbits 

 subcutaneously with that quantity of toxin corre- 

 sponding to i per cent, of the body- weight of each 

 respectively, and observe, if necessary, until the com- 

 pletion of one month. 



3. Inoculate a "control" tube of bouillon with a 

 similar quantity and incubate, to determine the freedom 

 of the filtered toxin from living bacteria. 



4. In the event of a fatal termination make com- 

 plete and careful post-mortem examinations. 



5. Repeat the experiments and, if the results are 

 positive, ascertain the minimal lethal dose of toxin 

 for each of the susceptible animals. 



The estimation of the m. I. d. of a toxin is carried 

 out on lines similar to those laid down for living bac- 

 teria (vide page 316) merely substituting i c.c. of toxin 

 as the unit in place of the unit "loopful" of living 

 culture. 



It frequently happens, during the course of casual in- 

 vestigations that a bouillon-tube culture is available 

 for a toxin test whilst a flask cultivation is not. In 

 such cases, Martin's small filter candle and tube (Fig. 

 161) specially designed for the filtration of small quan- 

 tities of fluid, is invaluable. This consists of a narrow 

 filter flask just large enough to accommodate an ordi- 

 nary 18X2 cm. test-tube. The mouth of the tubular 

 Chamberland candle 15X1.5 cm. is closed by a perfor- 

 ated rubber cork into which fits the end of the stem 

 of a thistle headed funnel, whilst immediately below 

 the butt of the funnel is situated a rubber cork to close 

 the mouth of the filter flask. When the apparatus is 

 fixed in position and connected to an exhaust pump, 

 the cultivation is poured into the head of the funnel 

 and owing to the relatively large filtering surface the 



