86 A MANUAL OF THE PENICILLIA 



are manufactured for this purpose). All discarded cultures should be 

 killed by heat. 



Mites 



Mites are brought into every laboratory engaged in the study of the 

 flora of raw products such as soil, cheese, mildewed textiles, etc. Rigid 

 isolation of the raw material brought in, with constant cleaning of the 

 working space, tools, and the hands of the worker, are the necessary price 

 for preserving purity in the cultures handled. Mites travel slowly, but 

 they keep going. They migrate from petri dish to petri dish through a 

 whole incubator and leave eggs, bacteria, and miscellaneous spores picked 

 up en route. They can go through cotton plugs, provided the culture 

 within attracts them, for they seem to avoid some species and destroy all 

 of other series. Some mites are so small as to escape notice by the naked 

 eye, others are easily seen. The presence of mites can usually be detected 

 by a characteristic odor in the infected cultures. 



Elimination of mites by sanitary measures is possible when rigorous 

 control measures are exercised. Stock cultures should be protected 

 against a possible invasion by mites. A satisfactory protective measure 

 consists in moistening the cotton plugs with the following solution: 



95 per cent alcohol 95 ml. 



Bichloride of mercury 0.5 gm. 



Glycerine 5 ml . 



Color with any of the aniline dyes 



The cultures must be allowed to develop into typical colonies before 

 poisoning and care must be taken that the solution does not come in con- 

 tact with the colony. An antiseptic formula for the purpose needs alco- 

 hol to insure penetration of the plug, a poison to destroy the mites, glycer- 

 ine to prevent the crystallization of the poison as the alcohol evaporates, 

 and a dye to insure the destruction of the cotton plugs when removed 

 from the tubes. The above treatment of cotton plugs likewise protects 

 cultures from invasion by certain molds which grow at low temperatures 

 and might otherwise grow through the cotton. 



Table tops and other exposed surfaces may be successfully freed of 

 mites by washing with an alcoholic solution saturated with paradichloro- 

 benzene and containing two to five parts of glycerine. Kerosene and 

 other selected petroleum fractions may likewise be used for this purpose. 

 They may also be used in the form of a fine mist to decontaminate incuba- 

 tors should these become infested. 



The same precautionary and control measures may be employed against 

 roaches and other small insects which often inhabit laboratories and some- 

 times infest plate cultures. 



