316 SUMMARY OF CUREENT RESEA.ECHES RELATING TO 



Employment of the Freezing^ Method in Histology.* — Dr. Axel 



Key and Professor Gustav Eetzius reproduce in German an account 

 of the freezing method which had been previously published by them 

 in Swedish. The method is in many cases of great advantage, but it 

 often causes certain abnormal appearances which, without due care, 

 might be taken for actual features in the tissue examined ; for example, 

 in fine sections of tendon cut when frozen and fixed afterwards by 

 means of perosmic acid, a series of longitudinal canals were seen ; 

 and in sections of brain a regular system of lacuna communicating 

 with each other appeared to exist which it was quite impossible to 

 demonstrate by means of an injection. All these appearances, in fact, 

 are produced by the freezing method itself; the water contained in 

 the tissues is driven out at the moment of freezing, and collects into 

 lacunae where there is the least resistance. It is evident, therefore, 

 that the greatest care must be exercised by histologists who make use 

 of this method. 



Improved Method of Using the Freezing Microtome.f — Prof. 



W. J. SoUas considers that the process of obtaining thin slices of soft 

 structures by means of imbedding in paraf&n has now been brought to 

 a state of almost ideal perfection ; on the other hand tbe method of 

 " freezing " still remains almost in its infancy. At present it is only 

 with great trouble that a continuous series of slices can be obtained 

 with it, and if these are cut from a loose disconnected tissue, they 

 break up immediately on being introduced into water to free them 

 from the gum in which they are always imbedded. Moreover the 

 waste of time involved in transferring from water to a glass slide is 

 simply appalling. 



Yet the freezing process has special advantages of its own. 



In the case of many tissues it affords a clearer insight into struc- 

 ture ; perfect staining is not so indispensable (provided, as is usually 

 the case, glycerine be used as a medium for mounting) : and when 

 hard parts occur in a preparation along with soft, both may be evenly 

 cut through with equal ease. It is not likely, therefore, to fall wholly 

 out of use, particularly for certain refined histological work, and 

 improvements may be confidently expected. 



The following may perhaps be regarded as a first step to others. 

 Instead of freezing in gum, as is usual, one uses gelatine jelly. This 

 is prepared and clarified in the ordinary manner. It should set into 

 a stiff mass when cold, how stiff will best be learned by experience. 



The tissue to be cut is transferred from water to the melted jelly, 

 and should remain in it until well permeated. 



It is then placed on the piston of a Eutherford's microtome ; the 

 " well " should not be filled, for adherence it is sufficient to roughen 

 the surface of the piston with a file. No more jelly should be used 

 than is sufficient to surround the specimen ; if too much has been added, 

 it may be removed when frozen by careful paring. 



When well frozen, slices may be cut in the ordinary way ; while 



* Retzius's Biol. Untersuchungen, ii. (1882) pp. 150-3. 

 t Quart. Journ. Micr. Sci., xxiv. (1884) pp. 163-4. 



