32 JOURNAL OF THE " [April, 



serve for a sufificiently delicate test of minute movements in the 

 outline of the protoplasm itself, which, in ordinary objects and 

 in tissue sections, might entirely escape observation. 



It is surely possible to predicate and classify the main causes 

 to which must be due the shrinking or swelling, distortion and 

 disintegration, which, sooner or later, are seen in progress within 

 the cells of most mounted preparations of organic material. 

 Thence we may deduce certain principles of selection or exclu- 

 sion, which we may apply toward the various reagents, mix- 

 tures, and solvents which claim fitness for this service. The care- 

 ful synthesis of formulae according to this system ought to clear 

 out of our way, once for all, a large number of unsuitable re- 

 agents; to put a stop to the concoction of merely experimental 

 formulae; and to bring us much sooner into possession of satis- 

 factory processes. It is now proposed to offer a brief statement 

 of the chief causes of alteration of organic structures, when im- 

 mersed in so-called fixing and hardening solutions and preserva- 

 tives. 



I. Alteration by Chafige of Natural Conditions or by Death. — 

 When we attempt to watch and unravel the lovely phenomena 

 •of life thrilling and pulsating within the field of the microscope, 

 great care and skill are needed to preserve those natural condi- 

 tions, within which it is possible, even in the living organism, to 

 recognize the normal forms and relationships of its structure. By 

 any change of temperature, produced by the heat of the room or 

 lamp, or the coldness of the metal of the stand; by lack or excess 

 of moisture, oxygen, or light ; by vibration or jar ; by offensive 

 vapors in the atmosphere, carbon dioxide gas from the observer's 

 breath, or the volatile solvents that are kept or used in the labora- 

 tory ; and perhaps by still more subtle but efficient causes of dis- 

 turbance, morbid and unnatural changes in the contractile mat- 

 ter may be produced which are difficult or impossible to avoid. 



But artificial trial by means of chemicals, as fixatives and 

 stains, by dissection and vivisection, however useful or indispen- 

 •sable for study of special elements, tends to be still more fatal to 

 accurate discrimination of protoplasmic forms in general mor- 

 phology. 



And, for this purpose, death ends all ; instantaneous coagula- 

 tion and alteration ensue ; our slow recognition of cadaveric 



