METHODS OF CULTIVATION. 165 



with success the experiment of Lister, the essen- 

 tial feature of which is the thorough cleansing 

 and disinfection of the urethral canal by means 

 of a solution of carbolic acid (5 per cent). The 

 glans should also be washed with the same solu- 

 tion ; after which the urine is passed into a glass 

 flask or test-tube which has been sterilized by 

 heat. This is at once closed with a plug of 

 cotton. 



Urine has been extensively used as a culture- 

 fluid, and is well suited for the development of 

 many species of bacteria; and especially for the 

 micrococcus, which has been shown by Pasteur to 

 be the cause of the alkaline fermentation which 

 ordinarily occurs in this fluid during warm weath- 

 er, within a few hours after its escape from the 

 bladder. It must be remembered, however, that 

 decomposition of urea into carbonate of ammonia 

 is also effected by heat, and that, consequently, 

 the composition and reaction of this fluid is 

 changed by boiling. For this reason its sterili- 

 zation by heat is objectionable for certain experi- 

 ments, and it will be necessary to obtain it from 

 the bladder free from bacterial contamination, by 

 the expedient above mentioned (method of Lis- 

 ter), or by means of a sterilized catheter attached 

 to a germ-proof receptacle, as recommended by 

 Pasteur. 



Aqueous humor, obtained from the eye of one of 

 the lower animals, recently dead, is a sterile albu- 



