MICROSCOPICAL AND PHYSIOLOGICAL EXAMINATION. 15 



In all experiments of this kind, organisms which have been 

 tested with some disinfectant should afterwards be brought 

 under the most favourable conditions of growth, otherwise 

 they will not develop, even though they be alive and capable 

 of development. In such cases, the ordinary temperature of 

 the room and solid nutrient substrata are not sufficiently 

 favourable ; it is also necessary to allow ample time for the 

 observation of such growths before definitely deciding whether 

 they are dead or not ; in fact, it often happens that they have 

 merely been somewhat checked in their development, and 

 that they may develop again, after some time, with their full 

 vigour. Furthermore, the temperature and the medium 

 in which the organisms are present when the disinfectant is 

 employed may be of some importance. Before testing a 

 culture thus treated, great care must be taken to previously 

 free it from all remains of the disinfectant by washing and 

 dilution. 



The first information on this subject we owe to R. Koch. 

 Subsequently, these researches were continued by Gruber and 

 others. 



Koch examined several poisons not only with reference to 

 the degree of concentration requisite for destroying bacteria 

 and spores of bacteria, but also with a view to ascertain the 

 particular quantity necessary for checking the micro-organ- 

 isms in their power of development in suitable nutritive 

 solutions. 



I will here briefly state the results obtained by Koch. 

 Carbolic acid was found to be a less efficient disinfectant than 

 it is commonly held to be. A solution containing 5 per cent, 

 destroyed the power of development of anthrax spores only 

 after 48 hours, whilst the anthrax bacilli were killed in two 

 minutes by a 1 per cent, solution. A solution of 1 part in 

 850 proved sufficient to check the growth of the bacillus, 

 and when anthrax spores were moistened 5 to 7 times with a 

 5 per cent, solution, their development was somewhat retarded. 

 A 5 per cent, solution of carbolic acid in oil or alcohol had 



