TOO MILK 



the milk, and to thoroughly centrifugalise it in a powerful centri- 

 fuge. The sediment is examined microscopically for the tubercle 

 bacillus, and the rest is inoculated into guinea-pigs subcutaneously, 

 as described below. It is advisable to inoculate several guinea- 

 pigs from each sediment, as some of the animals may die from 

 the action of the other bacteria present in the milk 1 . Professor 

 Delepine has shown that this accidental mortality is much 

 diminished if only quite fresh milk is used, or, if delay is un- 

 avoidable, when the milk samples are ice-packed during transit. 

 This mortality can also be diminished by treating the sediment 

 with antiformin before inoculation. 



Different authorities have advocated examining different 

 quantities of milk. The greater the amount examined the 

 greater the chance of finding tubercle bacilli, and the more 

 reliable a negative result. Delepine 2 , as a routine method, uses 

 two tubes of 40 c.c., and centrifugalises for a quarter of an hour 

 in a machine giving 3000 revolutions per minute. The cream 

 and all but 2 c.c. of the separated milk are then aspirated away, 

 and the separate residue from each tube, containing the sediment 

 and 2. c.c. of separated milk, after a microscopic examination of 

 the milk has been made, is inoculated into a guinea-pig. 



Other authorities use much larger quantities of milk e.g. 

 J- litre for each examination. Tubercle bacilli may also be 

 contained in the cream (being carried up with the fat), and to 

 complete the examination some of the cream may also be inocu- 

 lated, or, more simply, after a preliminary centrifugalisation 

 for half an hour, the cream may be thoroughly broken up by 

 a sterile glass rod, and the milk again centrifugalised. In this 

 way a large proportion of the organisms in the cream is 

 transferred to the sediment. In any case the sediment is 



1 O'Brien (Journ. of Meat and Milk Hygiene, 1911, vol. I, p. 295) found that out 

 of over 9000 guinea-pigs subcutaneously inoculated with milk sediment 33 per cent, 

 died, from causes other than tuberculosis, before the 28th day. Careful investigation 

 in the cause of this non-tubercular mortality showed that while part was due to 

 infectious diseases which the animals were incubating at the time of inoculation and 

 part to bacilli inoculated with the milk, the greater part must be ascribed to a 

 combination of factors, including the disturbance caused to the animal's economy by 

 the proteins injected and the consequent lowering of resistance to auto-infeclion. 



2 See Transactions of the British Congress on Tuberculosis, vol. II, pp. 286-7. 



