148 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



determined by a microscopic examination of films prepared in 

 the usual way and stained by a simple stain, such as carbol 

 thionin. A specimen should also be stained by Gram's method 

 and the results compared. The fact that, for clinical diagnostic 

 purposes, the examination of films is most important, and never 

 to be omitted, must be emphasized here. Serious mistakes, 

 such as the failure to find actinomycosis, etc., may often be due 

 to trusting to cultures alone. 



When cultural examinations are required, the best plan is to 

 make stroke cultivations on agar in the manner described on 

 p. 16, and incubate them for twenty-four hours at the tempera- 

 ture of the body. The appearances of the colonies will be 

 similar to those described as occurring in cultures made from 

 the blood, to which the reader is referred. It is to be noted, 

 however, that the gonococcus will not grow under such cir- 

 cumstances unless the surface of the medium has previously 

 been coated with blood. 



Another method is to make gelatin plates. This is a very 

 simple matter if the materials are at hand. 



Requisites. i. Two or three tubes of gelatin. 



2. Two or three sterilized Petri dishes. 



3. A platinum needle a loop will be best. 



Process. Inoculate a gelatin tube in the manner described 

 on p. 16, and then melt it by immersion in warm (not hot) 

 water. 



Distribute the pus throughout the melted gelatin by rolling 

 the tube between the hands, and by tilting it from side to side. 

 Do not shake, and do not let the melted gelatin touch the 

 cotton-wool plug. 



Take a loopful of the gelatin and transfer.it to a second 

 culture-tube. Melt the gelatin in this and mix as before. 

 Proceed to inoculate a third tube from the second one if you 

 think it probable that the pus is very rich in organisms. 



Now take the first tube and singe the projecting part of the 

 wool plug, and heat the mouth of the tube in order to destroy 

 any germs which may be upon it ; allow it to cool. 



Place the Petri dish on the table in front of yon, and raise 

 the lid sufficiently to allow you to insert the end of the test- 

 tube; do this, and tilt the latter so that the melted gelatin 

 flows into the dish. Immediately replace the lid, and tilt and 

 roll the dish until the gelatin forms an even film over its whole 



