38 L. S. ROSS 
of recent years, but problems of its morphology yet remain 
unsolved. 
The cytologist is confronted in his work by some obstacles that 
at present seem almost insurmountable. It is difficult for him 
to determine in all cases whether he is observing structures that 
are present as such in the living cell or whether he is observing 
artefacts. Do Nissl bodies, neurofibrillae, Golgi internal reticular 
apparatus, etc., have existence in living undisturbed cytoplasm, 
or are they the results of violent disturbances caused by reagents? 
Important as the answers to these questions may be as concerns 
the ultimate structure of protoplasm, yet is it really of vital 
importance to the cytologist in comparative work, provided he 
realizes and recognizes limitations? Does this lack of knowledge 
of necessity vitiate all his conclusions? That artefacts are 
produced by reagents is not doubted, but the difficult question is, 
what appearances are those of artefacts and what ones are not. 
Certainly, some conjectures based upon various experiments in 
producing artefacts are not warranted. Unquestionably, re- 
agents produce artefacts in albumen solutions, as reticulations, 
etc., but comparisons between the effects produced by reagents 
upon the cell and upon colloidal solutions in a test tube are not 
wholly justifiable. At best the results from such experiments 
can give rise to inferences of probability only. As a generaliza- 
tion, however, similarity of results indicates similarity of materials 
upon which the technic was used. Likewise, dissimilarity of 
results indicates dissimilarity of materials. The importance of 
the study of living and postvital, fresh, unfixed cells cannot be 
overestimated, as apochromatic objectives and the true vital 
dyes have enabled us to distinguish various elements of the 
cytoplasm under these conditions. 
If the cytologist finds that a particular appearance is pro- 
duced by the same technic upon cells from the same source, and 
also by a variation of technic, and if he finds further that cells 
from different sources respond similarly to the same technic and 
to variations of technic within limits, then he has a basis for 
cytological work upon cells of a specific kind and also for com- 
parative cytology—a basis, it is true, that is not so satisfactory 
