1889.] MICROSCOPICAL JOUBNAL. 125 



The potato is then laid in a i to iooo watery solution of corrosive 

 sublimate for about an hour. Afterward it is washed in water and 

 placed in the steaming apparatus, and kept at the temperatui"e of ioo c. 

 for a half to three-quarters of an hour. It is then allowed to cool under 

 cover from dust. In the meantime a couple of glass dishes, ope larger 

 than the other so as to form a cover, are washed out with i.iooo subli- 

 mate solution, and a piece of filter paper moistened with the same solu- 

 tion is placed on the bottom of each, so that when the one is inverted 

 over the other there is a moist surface at the upper and lower part of 

 the chamber. This is to keep the air moist so that the surface of the 

 potato does not dry. The potato after being cooked and cooled is cut 

 into halves in the following manner : a long flat knife is heated in 

 the flame and allowed to cool. The left hand is then dipped into i .1000 

 sublimate solution, and the potato is taken up with it. With the knife 

 held in the right hand a single sweep is made through the potato, and 

 the cover of the moist chamber being lifted, the two halves are sepa- 

 rated and laid down with the cut surface uppermost. The cover is then 

 replaced and the potato is ready for inoculation. In some cases, where 

 the potato is to be placed at the body temperature and kept for some 

 time, tall narrow vessels similar to those used by Koch for testing air, 

 plugged with cotton-wool and sterilized, and large enough to hold half 

 a potato, are employed. 



" The surface of the potato maybe inoculated by platinum wire, or by 

 a thin, flat knife, by means of which the material is rubbed over the 

 surface of the potato. The knife or needle is dipped in the cultivation 

 to be inoculated and drawn rapidly over the surface of the newly pre- 

 pared potato." 



Fluid cultivations have given place to solid culture media. There are 

 two serious drawbacks to them. One is, that if the} 7 should in any way 

 become contaminated the cultivation will be entirely spoiled, the new- 

 comers mixing thoroughly with the original bacteria. Further inocu- 

 lations, therefore, from flasks thus contaminated simply carry over the 

 two kinds. The second disadvantage is, that the original culture must 

 be started from a material containing only one kind of bacterium, it 

 being almost impossible to separate one form from another with fluid 

 media. 



In special cases, however, fluid cultivation materials have cei'tain 

 advantages, one being that they can be placed in an incubator at the 

 temperature of the body without the result being spoiled. With gela- 

 tinized media, however, this cannot be done, all melting at the tem- 

 perature of the body. Agar-agar (a material derived from the plant 

 Gracilaria lichenoides) is sometimes used in place of gelatine ; mostly, 

 however, to maintain pure cultivations of bacteria which grow at the 

 temperature of the body. Agar jelly is difficult to prepare ; moreover, 

 it is not as satisfactory as the other. 



Fluid media are also more serviceable than solids in experiments on 

 the growth of micro-organisms in different gases. 



Test-tube cultivations, plate cultivations, and glass slide cultivations 

 are the three principal modes of using nutrient jelly for cultivations. 

 The best temperatui-e for growth and for solidity is said to be from 20 

 C. to 22 C. At 25 C. 10 per cent, gelatine is just solid. 



Test-tube cultivations are employed when it is desired to keep .up a 



