542 Journal of Applied Microscopy. 



out the blood before it, the necessary pressure being secured by raising the funnel 

 to various heights as required. An injection of from thirty to forty seconds is suf- 

 ficient to insure the thorough removal of the blood, which is indicated by its no 

 longer escaping from the right ventricle. The pinch-cock G is now closed and F 

 is opened, and the fixing fluid is injected in a similar manner. Practically every 

 cell in the animal is thus instantly killed by direct contact with the fixing agent. 

 The fixing fluid is allowed to run through the system for from five to ten minutes, 

 after which the cannula is disconnected and further treatment adapted to the fixing 

 agent employed is proceeded with. For example, if sublimate has been employed, 

 the alimentary canal is opened and its contents removed, after which the animal 

 is brought into alcohols of increasing strength, the body having been so opened 

 as to permit free access of the alcohol to every part. Before or after the harden- 

 ing has been completed by the alcohol, the various organs may be removed and 

 placed in separate jars or bottles for further treatment and preservation. With 

 Zenker's fluid, after injection is complete, the various organs are brought into a 

 fresh supply of the fluid, where they remain over night, followed by washing out 

 with water and graded alcohols. 



By this method of fixation the exact normal relationships of the different 

 parts are preserved, and pieces may be removed and sectioned with accuracy 

 in any desired plane. For histological studies upon the nervous system, this 

 method of m toto fixation gives the most admirable results, and thorough and 

 equal hardening with the various bichromate mixtures is readily attained in a 

 much shorter time than is usually the case. In addition, the removal of the 

 brain and spinal cord is greatly facilitated by the firm consistency imparted to 

 them. 



By limiting the zone of action of the injection by ligating the arteries 

 passing to other parts, any desired portion may be fixed alone. This 

 applies with especial force to the brain and sense organs. The eye may be fixed 

 in situ, permitting sections to be made showing the most delicate histological 

 detail, without any of the usual vexatious collapsing. The internal ear also 

 may be easily and thoroughly fixed by this method. 



A number of useful modifications may readily suggest themselves to one 

 making use of this apparatus as just described. One of the most convenient of 

 these is the substitution of a glass three-way stop-cock for the Y tube and the 

 pinch-cocks above it. 



By substituting an isotonic solution containing no chlorides for the normal 

 salt solution, and limiting the injection to the abdominal viscera, excellent 

 preparations of endothelia may be secured. After the blood has been washed 

 out and the abdominal cavity has been rinsed with the isotonic solution, a one- 

 fourth to one per cent, solution of silver nitrate is injected. After an injection 

 of from three to five minutes, the silver nitrate is washed out with distilled water, 

 the mesentery is spread out and exposed to the sunlight until reduction is 

 completed. P\ M. McFarland. 



Histological Laboratory, Leland Stanford Jr. University. 



