Waksman 



156 



Actinomycetes 



cedures are utilized for the isolation of pathogenic actinomycetes from 

 infected plants. One of these (412) may be described as follows: 



Potato tubers are placed for 2 minutes in a mixture of fresh cal- 

 cium hypochlorite solution in water, made alkaline with sodium hy- 

 droxide. The tubers are then removed, and a slice is cut, comprising 

 the lesion together with some of the underlying tissue. This slice is 



Fig. 32.— Different forms of scab produced Ly S. scabies Qfroin Goss, 147). 



washed in sterile water and triturated in a flamed mortar with a sterile 

 pestle. The macerated suspension is transferred to a sterile tube and 

 one or two drops placed in the bottom of a sterile Petri dish. About 

 10 to 15 ml. of egg-albumin agar, which has been melted and cooled 

 to 45 °C., is poured into the dish, and the latter is rotated to distribute 

 the suspension through the medium. The plate is incubated at 25- 

 30 °C. Colonies of the pathogen develop in 2 days to 3 weeks, de- 

 pending on the strain of organism. 



Cmisative agent.— The organism causing the common scab of the 



