108 BACTERIAL DISEASES OF PLANTS 



per cent carbolic acid water, the former more than the latter. 

 Surfaces covered with a thick cork layer, e.g., potato tubers, 

 stand exposure to 1 : 1000 mercuric chlorid well (30 minutes) ; 

 thin green parts, such as pieces of leaves, should be exposed 

 to it only for a minute or two. Infected tools which cannot be 

 flamed may be dipped into the carbolic acid water. Carbolic 

 acid should not be used on the hands. Discarded culture-tubes, 

 flasks, dishes, etc., which are not autoclaved should be treated 

 wdth the chromic acid cleaning mixture before w^ashing. Rubber 

 gloves should be used in handling this mixture. Infected hands 

 may be washed in the mercuric chlorid water. The student 

 should remember that germicides are poisons, and should 

 govern himself accordingly. They must not be left where 

 children or animals can get them. Hands accidentally wetted 

 with the chromic acid mixture should be washed immediately 

 and thoroughly. 



Still Air. — I regard clean still air as very important. For 

 this reason I never make transfers in the open room, but always 

 under a hood or in a special transfer chamber, such as I have 

 described, and I do not advise its ventilation by means of an 

 air current. 



Clean Hands. — These are still more important. The aver- 

 age individual infects everything he touches, and also, as a rule, 

 touches everything within his reach. Hence the great prevalence 

 of contagious diseases! Apparently it is a necessary part of 

 the psychology of a great many persons to become satisfac- 

 torily acquainted with an object only through the sense of touch. 

 Deprived of touch such persons are almost as blind as the sight- 

 less. Until the student has learned to consider his hands, even 

 when ''clean," as never really clean but always as contaminated, 

 he has scarcely made a beginning in bacteriology. Your hands 

 should be kept out of media and also out of your mouth. 



To these preliminary remarks need be added only what is 

 said under the special diseases, and some general cautions. 

 The culture-room should be wiped up frequently with clean 

 water. Generally, one's coat should be removed and his shoes 

 cleaned before entering it. Fragments covered with^spores 

 of molds should never be taken into this chamber, nor should 



