INNOCULATION METHOD 167 



aged by squeezing them. This procedure reduces the resistance 

 of the glands and enables an earlier diagnosis to be made. 

 Dodd, 34 and Joannovico and Kapsammer 35 carefully studied 

 this technique and found it entirely successful. They found 

 that even doubtful cases could be diagnosed within fourteen 

 days. 



The microscopic appearance of the lesions is usually suf- 

 ficient to enable a trained observer to make an accurate diag- 

 nosis, but in all doubtful cases cover slips preparations should be 

 made and supplemented if necessary by histological sections. 

 For cultures, nodules are squeezed between two sterile slides 

 and the contents smeared over glycerine agar slopes. The 

 cultures are incubated at 37 C. 



For the differentiation of tubercular from other infections, 

 Anderson 36 suggested the subcutaneous injection of 2 c.cms. 

 of tuberculin. In a healthy animal a slight febrile reaction 

 occurs and passes off in a few hours, but this quantity of tuber- 

 culin is sufficient to cause death in less than twenty-four hours in 

 a guinea pig showing well developed tuberculosis. When the 

 lesions are slight the animal will become sick but may not die. 

 This method may be used as an addition to the usual autopsy 

 but should not be substituted for it. 



Even when the best technique is used, it is often found that 

 the experimental animals may die from acute infections within 

 a few days of inoculation. This is due to " dirty " milk and 

 can be partially eliminated by the treatment of the sediment 

 with 5 per cent antiformin for thirty minutes and finally 

 washing with physiological saline. Eastwood and Griffith 37 

 found that 10 per cent antiformin slightly weakened the tubercle 

 bacilli and that a 20 per cent solution almost destroyed them. 



Death of the inoculated animals after ten days, from infec- 

 tions other than generalised tuberculosis, is largely due to 

 improper attention to the housing conditions of the guinea 

 pigs. These must be kept isolated in clean cages with not more 

 than two animals to a cage and housed in well-ventilated 

 rooms. 



