INFUSORIA. 137 



some trouble in studying them as they are so lively 

 and so small. The stage of the microscope must be 

 kept in continuous motion to counteract the motions 

 of the Infusorium and to keep it in the field, so that it 

 may be seen as anything more than a whirling speck, 

 and high-powers are needed to examine it. But the 

 beginner's object will be gained if he learns to know 

 an Infusorium when he sees one, and if he learns the 

 names of some of the largest and the most common. 

 Many can be seen with a one-inch objective, but to 

 ascertain whether any special one has cilia or flagella 

 will demand a one-fifth inch or a higher power object- 

 ive, and unless this point is positively decided the In- 

 fusorium cannot be identified. But "it is only the first 

 step that costs." Any.- work or study is always hardest at 

 the beginning. When the student has identified one 

 Infusorium he will have little trouble with what comes 

 after. The attached forms will not be very difficult 

 even at first, if a sufficient magnifying power is 

 used, for since they are fastened by stem or by lorica 

 to another object, they can be examined at leisure. 



None of these delicate creatures can be preserved as 

 permanently mounted objects. Many chemical solu- 

 tions and mixtures have been recommended for kill- 

 ing and keeping them, but none is satisfactory, the 

 soft bodies going to pieces and melting away almost 

 as soon as after a natural death. If the observer is 

 greatly annoyed by the incessant movements of the 

 free-swimming forms, and desires to see how they 

 look when quiet for a moment, the following solution 

 will help. It answers the purpose well in some cases, 

 while in others it is worthless. It always kills, but 

 does not always preserve even momentarily after 



