Infectious disease is defined traditionally as the result of microbial activities and the rate of growth and multiplication of invading organism in a given tissue may be said to be the most important factor in the early stage of many infectious diseases among many factors in host-parasite relationship which may influence and modify the course of infectious processes.

The author considered it might be worthwhile to observe the fate of microorganisms in the joint fluid. The bacterial suspensions of Gram positive bacteria such as Staph. aureus, Staph. albus, B. subtilis and Gram negative bacteria such as Es. coli, Ps. aeruginosa were inoculated into the joint fluid from 14 cases of several arthritis of the knee joint and observed the viable units of the bacterial species after 1,3,5 and 7 hours of incubation at 37° C under aerobic condition. Results of the observations were summarized as follows:

1) The viable units of Staph. aureus began to increase significantly between 1 and 3 hours of incubation and then showed marked increase after 7 hours of incubation.

2) The viable units of Staph, albus began to increase moderately between 3 and 5 hours of incubation, but there was slight increase or almost no increase thereafter in all cases.

3) The viable units of B. subtilis showed abrupt decrease and could not be demonsetrated at all after 1 hour of incubation except one which also showed marked decrease.

4) The viable units Es. coli showed no remarkable change or slight decrease upto 7 hours of incubation.

5) The viable units of Ps. aeruginosa began to decrease significantly within 1 hour of incubation and thereafter could not be demonstrated at all except one which showed rather slight increase.