86 PROTOPLASM 



institute studies of my own upon the structure of protoplasm, 

 nevertheless I soon found myself forced to take this course. 

 I therefore made use of the time and opportunity which the 

 past two years have afforded me to collect further observa- 

 tions in this line, upon which I will first report briefly. 

 It should be noted at the outset that they were all carried 

 out with the aid of the best optical apparatus of the present 

 day, i.e. with the apochromatic objectives, 2 mm. Ap. 1'30, 

 and 1-40 of Zeiss, employed in combination with the 

 strongest compensating oculars 12 and 18. The large 

 amount of illumination given by the objective Ap. 1-40 

 permits perfectly well of the use of ocular 18. 



The structural relations are in general so minute and 

 delicate that the employment of the strongest powers 

 seems altogether indispensable. When the daylight, as was 

 so frequently the case, was not sufficient, a good petroleum 

 lamp (Hinck's duplex burner) was used as a source of 

 illumination, its light being concentrated on the mirror of 

 the microscope by a globe filled with water slightly coloured 

 with ammoniacal solution of copper oxide. The Abbe's 

 condenser was used in some cases, but not in others, since I 

 frequently remarked, as I thought, that finer structural rela- 

 tions came out more clgarly without it. Special attention 

 ought to be directed to regulating the strength of the illum- 

 ination of the object in such investigations, since it is 

 notorious that too intense an illumination obscures the details 

 completely. It is therefore very advantageous to be provided 

 with an iris diaphragm, and especially with the arrangement 

 permitting a vertical displacement of the illuminating 

 apparatus and of the ordinary diaphragm. I lay the more 

 stress on these points here, since I am convinced that many 

 results not in accordance with my own depend on insufficient 

 attention being paid to these particulars. 



1. Investigations on Protozoa 



Since the protoplasmic structures in even the highest 

 Protozoa can, in great part, be made out very well in the 

 living condition, I prefer to describe these forms first. 



