BIOLOGICAL RESEARCH. 



11 



growth or an individual, a single cell. In the first case, the 

 certainty of the result is determined by the purity of the 

 growth, and whilst the work is in progress this must be secured 

 by the adoption of special precautions to be further described. 

 In the second case, with which we now have to deal, the 

 entire examination must be carried out under the microscope, 

 special means being required to enable us to observe the series 

 of changes that arise from the development and growth of the 

 single cell. With this aim in view, Ranvier's moist chamber 

 may be used (Fig. 3). This apparatus is made by grinding 

 a slight hollow in the middle of a common object-glass ; round 

 this hollow a groove is made of greater depth to carry water. 

 The drop of nutritive solution, which must be very small, is 



Fig. 3. 



placed in the middle of the hollow and covered with a cover- 

 glass, which extends beyond the groove. When the cover- 

 glass is in place, it is cemented by means of vaseline, and the 

 drop is thus enclosed between the cover-glass and the hollow 

 of the object-glass, whilst the water in the groove prevents 

 evaporation. 



If by suitable dilution, care has been taken that only one 

 cell has been sown in the drop of water, the study of its 

 development may be extended for any length of time, with 

 the certainty that all forms that appear are derived from 

 one and the same individual. It is obviously a condition of 

 this and all similar investigations that the liquid and the 

 closed part of the apparatus must be sterile. 



This chamber may be used again to decide whether fine 



